That depends. Priests in troll culture aren’t really like your usual holy Light human guys. Mostly they are witch doctors, hexxer or some of the likes of hexx priests.
As just a troll priest you can take different roles. But mostly mending people and over all just revering your Loa / helping other trolls to connect to your Loa.
When it comes to powers you can go crazy. Anything death magic. Raise skeletons, throw bones at people, use magic that makes things decay. There aren’t really any limitations.
´https://www.wowhead.com/guides/reaping-strategy-battle-for-azeroth-season-2-mythic-affix´
Take a look at what the ghosts of Bwonsamdi (or himself) can gameplay wise do.
I can find things like: gravebolt and shadow smash. So you can really go wild on ideas that have to do with decay and / or death.
Though priests aren’t much to fight in troll culture. More to communicate with the spirits, the Loa and help people with their sacrifices to their Loa and such.
Gonk, master of shapes. He allows trolls to follow multiple Loa at once. Which is (most presumeably) the reason why zandalari druids exists and can shapeshift.
And
`https://wowwiki.fandom.com/wiki/Troll´
To learn the different histories of the troll tribes.