I think they're all grammatically okay, but the second two constructions are very unusual. Such a phrase is normally constructed like this in colloquial conversation:
Who are you, really?
Who are you, actually?
These questions would be asked by someone who has suddenly become aware that someone else is not who they previously said they were.
Who exactly are you?
This construction is common involving the word "exactly" specifically. I've seen the other construction used with "exactly" as well. The difference in meaning is slight (and the three sentences could likely be used interchangeably without anyone noticing) but this phrasing suggests more that the speaker is merely confused, not deceived. For instance, a story about the American comic book hero Superman might show him in his civillian identity, lifting a car over his head, at which point an amazed bystander might ask, "Who exactly are you?" The word "exactly" suggests that the speaker had a vague idea of who the person was before, and that needs clarifying. "Really" and "actually" suggest that the person was falsely someone else, since we are now asking for the "real" or "actual" identity of the person.
Ditto Joe. Let me add:
To "enlighten" is to give information or wisdom. To "inspire" is to motivate.
"Enlighten" is rarely used today. But an example of a correct usage is, "I didn't know about the new rules until my boss enlightened me."
Perhaps somewhat more common is the adjective "enlightened", meaning "wise" or "compassionate". Like, "Tsar Alexander considered himself an enlightened monarch."
An example sentence with "inspire" is, "I was inspired to buy a new car by the desire to impress my girlfriend."
They're not really the same thing at all. I could get new information and do absolutely nothing about it, I might just say, "yeah, whatever". I could be inspired without getting any new information. Perhaps someone just encouraged me.
Where they might somewhat overlap is that "inspire" can be used to mean that one idea led to another. Like, "Mr Smith's latest novel was inspired by a story he read in the news." He got some idea or information, and that idea led to another idea.
But I can't think of any sentence where you could substitute "inspire" for "enlighten" or vice versa without significantly changing the meaning.
Best Answer
Short Answer:
Aside from the third one (with how), all your sentences are correct and mean the same thing. The fourth (with like) is informal, and not normally used in serious speech or writing.
Long Answer:
All your sentences consist of two clauses, a main clause (I'll do it), plus a subordinate clause (he did it), and your question is about the terms that can join these two clauses, i.e., about subordinate conjunctions.
Let's take them one by one. The third is the only tricky one, so I'll save it for last.
This is the first definition OED provides for way:
As you can see, your first sentence perfectly fits this definition and its examples:
This is a valid usage of way, among other constructions that you can use after this word. I don't think anybody's called way a conjunction, but in your sentence it acts like one, because of the hidden that which I hinted at in the parentheses.
As, simply, is a conjunction,
Look at its definition: "...the way that something happens ..." . It suggests that there should be no difference between choosing as or the way in your sentence.
Like can be used as a conjunction too, but some people consider this use to be incorrect. We don't have to go that far, because it's so widespread in the informal register that you can't say it's wrong. It's just informal:
Notice the as in the definition. So up to now we have three equivalent terms to use as a conjunction. (Watch out for the informality of like (instead of as) though!)
How is the tricky one here. It's certainly used as a conjunction sometimes, as in
But is it used for comparison? as in
Well, Michael Swan in his book Practical English Usage says no, we can't use how this way:
So, aside from the third one (with how), all your sentences are OK, without any significant difference in meaning.
You can take a look at this Ngram diagram too:
See the hits for "do it how he". Almost none is relevant.