Witcher 3 secret ending

As it turns out, not only if you attempt to romance both Yen and Triss, and get Ciri to further her witcher training, there is 1 vital quest that you must under take.

But Roxi wont tell me what it is 

This came about after working on something with Mel, then i thought "if i dyed her hair black, eyes purple, shed make a hot Yennefer." 

And of course i had to include Roxi as Triss and Cassie as Ciri