Learn English – What’s a word for a group of questions asked together

Another good word would be reticent: inclined to be silent or uncommunicative in speech.

Q1: Is it jealousy of sth or jealousy at sth or jealousy about sth when referring to the reason why someone is jealous?

I would think you would use the same prepositions for jealousy as for jealous.

Paul was jealous of Bill. Paul expressed jealousy of Bill.

Paul was jealous for/over his wife. Paul expressed jealousy for/over his wife.

Paul was jealous for/over Bill's car. Paul expressed jealous for/over Bill's car.

_{Somebody correct me if I'm wrong, but I believe you can use either for or over with jealous in either of the latter two senses it holds above.}

I have never heard that you could be jealous at something or about something, but if the usages are valid, I would expect that you could use them in the same with jealousy.

Q2: Is it common to say jealousy of sb when referring to the person of whom I'm jealous?

Jealousy of/for/over/at/about something is awkward and in my experience little-used. It is more common to say, "I am jealous of him," as in the example first sentences above.