What are the differences between these sentences ?
1.I asked him on an opinion.
it sounds like I wanted to know his thinking directly related to an opinion for a long time.
2.I asked him about an opinion
it sounds like I wanted to know his thinking both directly and indirectly related to an opinion for a long time.
3.I asked him of an opinion.
It sounds like I wanted to know his evaluation on the quality of an opinion for a short time.
4.I asked an opinion of him.
it sounds like I required him to give his opinion.
5.I asked him an opinion.
it sounds like I gave him an opinion so as either to hear his thinking of, about or on an opinion OR to have a talk with him on an opinion.
6.I asked him for an opinion.
it sounds like either I required him to give an opinion(presumably in this case an opinion should be his opinion) or I required him to speak of or about an opinion, or I required him to talk with me on an opinion.
This sentence shouldn't be used widely, because of corruption of a variety of interpretations.
- I asked him over an opinion.
it sounds like I wanted to know his thinking broadly for a long time.
I think this post would be very helpful for learners to grasp the tiny differences between their meanings.