The oil filter is under a small cover that has 3 bolts holding it on the right side of the motorHonda trx 300 oil filter?
Make sure you put it in in the right direction or you will damage the engine
george b is right, I know it sounds stupid but I have seen many Honda engines go because someone installed the oil filter backwards, even techs at the dealerships!
On the right side of the engine. The filter is inside the little cover with 3 bolts.
we take ours to a HONDA Dealer..And have it completely checked over