Learn English – Use “motivation for learning English” or “motivation in learning English”

"In" or "at" are both acceptable to specify a stage or point in time. "On" is less used for that purposes, and tends to be more informal. Someone might say "We're on learning the alphabet in Chinese class", but it would be less likely to be written in a more formal sentence, like the one you've given as an example.

Incidentally, alphabet is singular when you are talking about only one set of letters (the "English alphabet"; but "the Greek and Tamil alphabets").

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.