You mean "finally" or "last but not least". "At last" is not what you mean. "at last" has a different usage e.g. After travelling all day, at last, we reached our destination at 10pm." "At last" indicates that you are relieved that something has finished. "Finally" is neutral and does not have the same feeling associated with it.

" At last, he likes playing basketball? " Tom has many hobbies like watching TV , etc. , with playing basketball as his least favorite . Tom has many hobbies. He likes watching TV , etc., and at the very end of this list of favourites is playing basketball .

Yes, this sentence is grammatically correct.

Also he likes..... at last means finally,