Part 1
I haven't known him yet.
The grammatical form of this sentence gives the sense of a one-off completed event. The word that makes this so is 'yet'. 'Yet' means 'so far'. So 'I haven't known him yet' means 'I haven't known him so far' or 'up until this point in time'.
Thus we might say, "I haven't kissed her yet" or "I haven't met her yet."
Both of those refer to an event that has a start and a finish. However, with knowing, it tends not to have a finish -- once you know something, you know it forever. (Alzheimer's or death excepted)
For this reason, the grammatical form of "I haven't known him yet" encourages us to think of a discrete event that has not yet taken place. This promotes the Biblical interpretation of the verb 'to know'. Therefore I would tend to read it as an old-fashioned way of saying "I haven't had sex with him yet."
Maybe your teacher prefers that you don't learn about archaic uses of the verb at this stage and so has excluded that possibility.
Full Definition of KNOW
transitive verb
1
a (1) : to perceive directly : have direct cognition of (2) : to have understanding of (3) : to recognize the nature of : discern
b (1) : to recognize as being the same as something previously known (2) : to be acquainted or familiar with (3) : to have experience of
2
a : to be aware of the truth or factuality of : be convinced or certain of
b : to have a practical understanding of
3
archaic : to have sexual intercourse with
Merriam-Webster
Part 2
My question is whether I can say these three sentences: I haven´t know him yet that long,I have known him for two years and I have known a lot of people not speaking English very well.
Firstly I'll correct the sentences.
I haven´t known him that long yet.
I have known him for two years.
I have known a lot of people who didn't speak English very well.
I haven´t known him that long yet.
This sentence is correct. Knowing someone for a length of time is a discrete event. It starts at some point in time and ends at another point in time. It might occur in the following conversation:
"How long have you known John for? Is it over a year?"
"No, I haven´t known him that long yet. In fact the anniversary of our meeting is next week."
I have known him for two years.
Again this is correct. A period of two years has a beginning and an end. Thus 'for two years' describes the length of the period you have known him. The use of present perfect tells us that the end of the period of time in question is now. If the sentence had been, "I knew him for two years" then we understand that you no longer know him (maybe he died or left the country).
I have known a lot of people who didn't speak English very well.
The impression given by the sentence is that you used to know these people or you knew them for a short while but you no longer know them. Your acquaintance with them is over.
I hope this helps.
First past perfect and pluperfect refer to the same tense. They are synonyms. Look up pluperfect in any dictionary to verify this. Here at onelook dictionary are more than two dozen dictionaries to get you started.
Second, please see this answer to When is the past perfect exactly needed? It does a terrific job of stating when the past perfect (or pluperfect--they mean the same thing) is necessary.
In general your sentence 1B is grammatical, but it represents rather an incomplete thought. And it is not necessary to use the past perfect/pluperfect tense here. The present perfect or simple past would both be better choices, because they would not represent incomplete thoughts.
Your 1C adds more information to the response but still either the present perfect or simple past would be more common. You don't need the past perfect/pluperfect there because it is clear from logic which past action happened first, namely that you called him first.
In 2B, there is no reason for using the past perfect/pluperfect tense. The simple past is fine. You mention only one past action. And in fact both uses of the verb order refer to that same past action. It would seem strange to think that one occurrence of the same past action can come before another occurrence of the same!
The first sentence of 2C is grammatical But by itself gives an incomplete thought. There is only one past action mentioned, and it occurs two days back. Thus the simple past is better here because you are talking about one action completed in the past. Having us wait until the second sentence to hear the most recent past action (Yesterday when I opened the box) makes it awkward.
The second sentence of 2C is the only sentence in which the past tense/pluperfect tense is used in a way that is intended. You have two actions and you place one of them before the first one. This is pleasant sounding and appropriate.
For example sentences and a much better explanation, see the answer I link to above. And thanks for asking such a good question.
Best Answer
You cannot use I haven't known that here. The present perfect describes a present state which arises out of a prior eventuality, and you are implicitly saying that your present state is that you do know that—which is not a state that can arise out of your previous ignorance. (It can emerge from your previous ignorance, but it can only arise out of learning it.)
You may use I didn't know that, with or without until you mentioned it. This states that in the past you were in a state of ignorance, a state which ended at the point when your addressee mentioned 'it'. Until marks the end of a state, as explained here.
You are not obliged to include anything like until you mentioned it in order to make it clear that now you do know that—the discourse situation takes care of that—it serves only to make clear that it was your addressee's statement which dispelled your ignorance, not some other past event.
You may also use I hadn't known that, again with or without until you mentioned it. The past perfect does not necessarily describe a state arising out of a prior eventuality, because the past tense-domain does not have the contrast between simple past and present perfect which exists in the present domain—the past perfect serves for both. Here the past perfect acts as a “past-in-past”, analogous to the present-tense-domain simple past, so it describes a prior state of ignorance which ended at your past reference time, the time explicitly named in the until clause.
However, as you know, FumbleFingers' Perfect Truism instructs you that if you do not need a past perfect you should not use it. In this case there is no evident reason why a past perfect should be needed; consequently the best choice here is the simple past: