Alliance player and have my leatherworking maxed at 150 for the moment… The Expert trainer in SW says he has nothing else for me to learn…
Who do I see now to raise to the next level?
You have to go to the one in Darnasus.
Trainers will usually tell you who to go to next if they can’t teach you anymore.
Check out wow-professions dot com. They now have a Classic section for every profession.
Most crafts have 2 trainers locally for 1-75 and 76-150. Then they have 1 or 2 for 151-225 and 1 for 226-300.
Leatherworking (Alliance): 151+ go to Telonis in Darnassus (leather and tailoring in same building, LW is up on the higher floor)
Leatherworking (Alliance): 226+ go to Drakk Stonehand, in the main Wildhammer Keep in the Hinterlands. That’s the alliance dwarf stronghold at the west end of the zone. You can get there using the valley path up from Hillsbrad.