Yago

I can't meet a mage Yago, I was in Low Iantern at diferent times - morning, evening, night...

[Silverblade]

If Yago is not here then I can't help you much but where he should be is in the Low Lantern on the second deck down and to you left in a room on his own.
Go onto the upper deck from the docks and down the stairs, go down another flight and then proceed left as far as you can go, you should see a mage dressed in green robes, this is Yago. You must have agreed to get his spellbook to save another mages child for him to be interested. Her name escapes me but she can be found just North of the Splurging Sturgeon. Talk to her first if you haven't done so.
Otherwise ransack the room I just gave you directions to, I think the spellbook should be in the cabinet there.

The spell book is on his body I believe, so you probably won't find it in a cabinet.