I am considering buying the Panasonic Lumix GX85 and would like to know if I can use my Yongnuo YN968 EX-RT flash with it.

You might be able to use it as a manual-only flash.

Are they compatible?

Well, both are ISO-compliant, so you can put the flash on the hotshoe of the camera and fire it in sync. And the sync voltage is low enough that your camera is safe from the flash. But firing in sync is all the GX85 could tell the flash to do. Any power settings would have to be made on the flash itself, in M mode.

Will I get TTL with this combo?

No. Also you won't get HSS, or camera menu communication. If you want full TTL/HSS compatibility, you need a flash that's compatible with four-thirds/micro four-thirds. You can use flashes from both Olympus and Panasonic (the hotshoe protocol is included in the four-thirds standard), such as a Panasonic FL360L/Olympus FL600R (same flash, really).

But you can also get a Godox TT350-O or TT685-O, or flashes from Nissin or Metz. Yongnuo only makes Canon and Nikon TTL gear at this time. They say they're going to release Sony gear, but have made no announcements for Fuji or micro four-thirds. Godox is very popular because they have built-in radio triggering, but are a lot cheaper than the top-of-the-line OEM flashes that have radio triggering (e.g., an Olympus FL700WR).

There is a drawback with Panasonic and Godox gear, however: HSS banding. While the Godox -O flashes seem to work just fine in HSS with Olympus bodies, it's not quite as smooth on the Panasonic side. But the other functions, TTL, remote power/group control, works just fine.