Where does a lvl 39 THM grind?

[Jocko]

There is no longer favoured mobs or locations as monsters have basically been made equal to one another.

Grab some friends, find a place with lots of mobs and chain the shit out of them.

Yeah, that's the problem. My linkshell is dead, and shouting in Uldah for an hour has never gotten me a party. I suppose that's the price I pay for playing on Melmond

[Choyi]

Try peacful mobs such as diremice(check wiki for locations i know some are around Iron lake but not sure they're close enough to chain nicely), sheep, antelopes etc.
They are probably some of the most harmless of mobs in the game, my best tip however is just to set out and explore and experiment.

Like others mentioned find mobs that are at your level or just around (not much higher then 1-2 ranks, lvls scale alot more now) and try pick mobs you feel comfortable fighting.

This all also depends on what abilites traits you have avaliable not only from your main class, adjust for what you can tackle without downtime, if you struggling with even match (your level mobs) try mobs a few levels lower.

For example I found killing lvl 40-42 mobs on my lvl 46pug was a real breeze (no downtime and they kept spawning on me and linking as i fought so I just started aoeing them down) and they still gave around 200 exp per kill, was getting roughly 13-15k an hour or so.
Note that mobs lower then your wont give exp chains but like said adapt for what you can handle, in the end if you can avoid downtime the exp/h should be good all the same.