To what end. Yeah. The inevitable question. But more than that, Geralt just wants to know what Istredd's agenda is. Beyond knowledge, which tells him nothing.

There's no indication Geralt is particularly satisfied with Istredd's response, though he doesn't appear to dismiss it, either. It's about what he expected. Noncommittal. An answer that isn't an answer.

But though Istredd may not know where he stands, Geralt does.

"This is my home," he replies. "I won't compromise it."

And that includes prodding at supposed gods and toying with powers beyond their understanding. He's found a place in Abraxas that he'd not had at home. Somewhere Ciri can stop running, where his path is not lined with rumours and fears of Witchers. He likes it here. It isn't perfect, but it's theirs. There is no going back. Not for him. Certainly not for Ciri. If protecting this place and the Singularity is what will keep Ciri safe, then that's what he'll do.