She is being held as a prisoner in Oribos, and being interrogated by the Knights of the Ebon Blade about the Jailer’s plan.
https://wowpedia.fandom.com/wiki/Sylvanas_Windrunner_(tactics)Read the “Post-cinematic dialogue” section.
It’s really weird how nobody has given you the right answer so far.
Edit: Well, someone did. I missed it.
Um, that’s Malfurion.
She’s now a banana. Or maybe an orange. I dunno.
Or maybe the people who does know realizes how absurd is that the person who 1v1 the freaking Lich King and wiped the floor with him, is now being held in Oribos by a bunch of essentially nobodies (Don’t even try to say Morgraine could do something against her if she wakes up).
Instead, it’s better to imagine that she was put in cryogenic sleep to wait until the purge it’s done, and the patch comes out to compete with a whole xpac of a very popular game (lol).
Not so much where is Sylvanas, but when…
She was hopped up on Jailer Juice when she did that. Presumably, he’s now cut her off from his power and she’s back to being a stronger-than-average Banshee.
Oh they even went as far as to add that?
Was that after the backlash over the cinematic or before? I’m just wondering so I can laugh at the fact that Blizz keeps relying on afterthoughts for their storytelling.
Because many of them are in fact, trying to be funny rather than factual. Some of them are actually succeeding. The idea of an ‘unused npc waiting room’ is hilarious…and Malfurian being mistaken for a potted fiscus is just icing on that cake.
Hahahhhahahahhhahhahhaahahahaha.
Thank you, I need a good laugh today.
Hopefully a Banana. I don’t care about potassium.
But turning her into an orange would ruin citrus for me forever.
?Prove too useful to be jailed and rightfully take her place among elven kind as their supreme leader?
He was a beautiful, innocent creature! What did he ever do to you?
Wait and see.
Blizzard is also making sure those picture are turn into fruits…
I heard she went over to Final Fantasy 14.
The devs are trying to find a way to end this game for good, and it involves the Sylvanas character.
My inside sources tell me they plan to do a “What-If” style storyline with Sylvanas killing the everyone in the universe. The last scene has the titular character stating that “it’s finished, I can rest…” at which the screen fades to black with Sylvanas kneeling over the corpse of the player character and you’re redirected to a link to start your journey again in Classic.
Never forget 
He wasn’t the hero we deserved but he was the hero we needed
Rip 
old soldier 
Of course you would post this on an Alliance toon.
My guess is she’s on Archerus or whatever that fying necropolis is called that the Ebon blade uses as a home base.
I could be mistaken but I think the voice actor for him changed between Wrath and BFA, personally preferred the Wrath voice. Sounded more like a tired old man to me which seemed more fitting to the “Old Warrior”.
But who knows maybe that’s just nostalgia talking from his scene where he picks up his son’s body, the son he failed to protect in the end.