What is the best profession for a warlock?

Answer 1

The answer to this question depends a bit on what you want to do with the character. Regardless, I would suggest gathering professions (mining, skinning, herbalism) until level 80 to make some money on the way.

Raiding

There are a few major lines you could follow when raiding. Tailoring/Enchanting is a solid combo, and you can level enchanting by leveling your character up through the dungeon finder and winning disenchanted gear. Jewelcrafting provides nice passive bonuses, but will be less valuable at the start of the next expansion. Engineering has a lot of abilities to customize yourself, including a good Haste boost on gloves.

As a raider, you'd want to avoid Inscription, Skinning and Mining since they do little for you. Herbalism's ability "Lifeblood" has been changed to give you a Haste bonus, which might make it appealing as well as a moneymaker.

Since Warlocks only wear Cloth armor, the uses of Leatherworking and Blacksmithing are extremely limited.

PvP

Engineering has many "get out of jail" cards, but some are not usable in arenas. The Stamina bonus from mining may be worth it, and dovetails nicely with Engineering. Mining/Jewelcrafting provides solid bonuses as well.

Enchanting is also good in PvP because it allows you to enchant your rings with Stamina or Intellect (Spellpower). Combining Enchanting and Engineering seems a powerful option.

Alchemy provides a boost to consumed flasks and potions, meaning that if you used a Flask in PvP it lasts for multiple Battlegrounds, and the potions give a bigger boost.

Again, Leatherworking and Blacksmithing, while giving some passive bonuses, do not offer more than that due to the restriction of Cloth armor on Warlocks.

Soloing old content

Engineering is a winner here, because it gives you several teleporters to the old world, a portable mailbox and a repair bot (Jeeves). This way you can sell stuff you find as well as keep your gear in shape. If you find something useful (recipes, BoE stuff, quest items) you can mail them to your bank alt and keep them safe without wasting inventory space. If you don't have the key to a place, you can blow them open with seaforium charges.

For old content, Skinning and Mining may be good, because a lot of old content features nodes in instances or skinnable mobs. Enchanting is good if you want to disenchant old materials and sell them - but prices vary by server so your mileage may vary.

All other professions provide solid bonuses (except maybe Blacksmithing which only offers extra gem sockets and keys to open locks) but nothing specifically suited to old content.