Sometimes people smell of things strongly enough that Lambert could (to a limited degree) track them or know they've recently been somewhere. He's nothing like a bloodhound -- he can't pick up on personal, unique scents, and could be thrown off easily -- but if there's an object or scent strongly associated with a person, he can detect that.

He can also detect magic with his medallion.

Strange: Smoke and crazy wax. HELLA MAGIC
Childermass: Smoke and cheap tobacco. NOT AS HELLA MAGIC. Now with bonus pine and snow from being a changeling, oops.
Ginko: Mushi repellent and bad life decisions
Rita: Bit like fire, UNWASHED TEENAGER. MAGIC MAGIC
Tyki: HELLA MAGIC, weirdly blood