how do i get 300 alchemy so i can start transmutation master quest?
The alchemy trainers in any of the faction cities will train “Vanilla” alchemy. It’s a bit weird, as those same trainers also do Cataclysm alchemy, and the recipes are sorted by level, not expansion so the Vanilla recipes won’t sort to the top of the list until you can actually learn them. (It’s just a weird interface thing, you don’t need to learn the Cataclsym stuff to do Vanilla.)
You’ll need a selection of herbs from the lower zones. A lot of them are super cheap on the AH, so unless you’re trying to level up herbalism on a character it’s probably more efficient to buy what you need. Google should get you some actual guides with lists of what you’ll need. (Make sure it’s for retail and not classic — while a classic guide will probably get you there, it probably won’t be the most efficient path.)