He recently wore his new shirt which was a present from his aunt to the reunion

If you are asking someone to proof-read this sentence, than I will try.  You're sentence is almost correct, but you need a comma after shirt and aunt.  This is because the phrase from your sentence "...which was a present from his aunt..."  is a little cut in the sentence, it's not a complete part of it.  So if I say "I caught a purple frog, knowing it was poisonous, from the pond."  I can take out "knowing it was poisonous"  and just say "I caught a purple frog from the pond."  You can do the same thing with your sentence, saying "He recently wore his new shirt to the reunion."  Your added phrase "which was a present from his aunt" needs to be in commas, because you added it a bit to the sentence.  It's hard to explain, but it's just what happens.  :D  I hope I helped.