Some of the ways are obvious. For one thing, ask him about himself every chance you can.
Hint 2
He's really evasive, however. Half the time he changes the subject, and the other he just flat refuses to answer at all. So maybe we should ask someone else, like your friendly neighborhood Cathedral contact, Ewan.
Hint 3
But there are also some things you can do yourself. At some point after you've been to Loch Lomond --
-- you'll walk into the train station and find Alec gone. Unfortunately, he took his bag with him, but there's something else near his usual spot for you to find.
Hint 5
Turn your back on his chair and -- what's that blue thing in the shrubbery?
Hint 6
There's a partial note in the bush opposite his chair that leads you to a puzzle nearby.
-- you'll have a bug (in this case, a listening device shaped like a housefly) in your inventory. Ideal for listening in on Alec's conversations when you're not around to be evaded.
Hint 10
Leave the train station and go do something else. When you come back to the train station, watch Alec's spot for a time when he's gone but his bag is sitting there, then nip over and pop the fly in his bag.
Hint 11
To listen in, go to the cabin and use the "bug" icon on the computer. You'll then want to have a leetle talk with Alec about what you learn.