How did mourain knew about mat

[pratyaksh]

How did mourain knew that mat had all these memories?

When she mentions to Rand that mat maybe the patriarch of us all and something like that

[Thrasymachus]

We don't know exactly how Moiraine comes to know of Mat's memories from the 'Finn, but there are a couple of places where she could have learned of them. 

 

The first being where she goes through the redstone doorway in Tear, to get answers.  We don't know what questions she asked, though it doesn't seem likely that she asked about Mat, it is nevertheless possible that she asked about three ta'veren being so closely linked, and learned about it there. 

 

Then there's the rings ter'angreal in Rhuidean, where she lived out all the variations of her life.  In at least some of those variations, she would have learned of it, and could have retained that knowledge from there. 

 

Then there's all that time she spent as a guest of the 'Finns courtesy of Lanfear.  She got three boons from that, but we only know of the one: her angreal bracelet.  It's possible that one of the others could have included knowledge of what Mat got. 

 

And, of course, there's Mat himself.  She, Thom and Mat would have spent at least a little time together after her rescue from the Tower of Ghenjei, and Mat would likely have wanted to explain himself, as to why they took so long to come get her, and what his worries were in making their plans.  He may also have wanted to get some reassurance from her about those memories, and what they mean regarding his ongoing ties to the 'Finns, since she's the only Aes Sedai he might suspect knows anything about it and would trust enough to ask.

[Sabio]

She knew about Mat alot earlier then her rescue.  She mentioned to Rand about if certain things were considered Mat would be the oldest of us all or something like that.  I don't remember the exact quote.  

[pratyaksh]

I actually found out how mourain knew.

Thom told her.

In knife of dream mat told Thom about his memories