Normal trials typically need 1 tank, 2 healers, and 9 DPS/DD. PUGs usually have a hard time getting a tank or two healers (in my experience). The Craglorn trials are pretty easy, nHRC can see some boss wipes if you're not careful. But nSO and nAA are very straight forward and easy. Some people require TS or Discord, but I've never been in a group where I felt it was needed.
If you do Maw of Lorkhaj, nMOL can be a tricky boss fight, and some PUG leaders are a little unforgiving if you have a role outside mash damage.