How do I play a friend in NHL 20

Yup, Aljo is correct - Modes that allow for direct competition between friends utilize a simple add player function with lb/l1.

EASHL allows friends to play but the game will be unranked and you're forced to use seperate 2v2 teams to make it happen.

It's possible to match up with a buddy in ONES but you both need to be in the same round and have to start random matchmaking at the same time - your chances of matching up (depending on off-peak and peak hours) can still be slim