Learn English – Is “to have one’s head in the sky” a valid English idiom

When you "raise a point", you are bringing up an issue to be discussed. After someone has raised a point, you can refer to it as "the point [that has been] raised."

One possible sense of take is consider, as in "take, for example, the lowly worm." (You are not being asked to physically acquire a worm, but to think about some aspect of it.)

Thus, when you want others to examine the issue that someone brought up, you can ask them to "take the point raised".

Your intuition is right. The customary preposition there is “at”:

I am learning the ropes at my new job.

This search on Google Books brings up 2,700 results.

The reason for “at” is to indicate a location without regard to its shape or structure. If you imagine the job as a location, there are metaphorical “ropes” there which you have to learn. At other locations, “the ropes” are different.

It’s natural to say in or of when referring to a subject or a skill:

Very few people will help you learn the ropes in science.

Learning the ropes of science can take many years.

A job naturally has a location, but science doesn’t, so “at” would sound wrong there.

This search on Google Books brings up 7,850 results.

You can say this:

I am learning the ropes of my new job.

but it suggests that by “new job” you mean the occupation in general, not the specific place where you work. For example, you might learn the ropes of real estate by learning the ropes at Century 21. It's not wrong to say that you’re learning the ropes of Century 21, though.