I haven't tried on the latest version, but previously was simple.
Arouse her, then kneel or slide (any crouching position). If she doesn't start the oral with you on that position, youcan use grab it, and start yourself
If you initiate anal you are likely to be knotted within two turns, which results in an end to battle and potentially a game over.
If you look at the side menu during battle that lists potential endings, there is one to be knotted orally as well, and iirc, it's supposed to be an automatic game over.
I know how to get oral started, and she even swells up like the knotting anal position, but it never seems to initiate the knotting oral sequence.
Yeah, there's something weird going on with the current code. I tried to force myself to lose orally to the goblin (both of then) and the scene didn't happen.
I even reached a point where i destroyed the goblin's will and it was just laying on the floor with 1hp, zero stamina and the dick hard every few turns, and i was sucking dick until the ends of times.