Demand:exactly what I said in the previous exchange.
There was never a "demand", Triss always volunteered the help.
an insistent and peremptory request, made as if by right
ask authoritatively or brusquely.
Can you tell me? is a question. Tell me everything is a demand. Nothing else to say on that, really.
And yes she did volunteer, after lying and telling Geralt she was the love of his life. Seems kind of sketchy for her to only volunteer to help after he starts piecing stuff together. Triss told her own edited version until they had a long conversation about the whole thing and Geralt insisted on knowing everything, even the stuff she doesn't want to tell him. Still not sure what is in question here.