My name is on the mortgage (not my son),my sons name is on the deed with mine, son lives at the property full time,pays the mortgage/taxes. Who can claim what for taxes?

My second home bought 2018, I own the mortgage.  Son lives in home, pays all expenses including mortgage.  Son is on deed with me.  What do I need to claim on taxes?  As a second home?  Can son claim mortgage interest, taxes on tax return?  I am a bit confused about a gift tax?