In doing the quick research I made a list, but it's in swedish so I'll have to translate it I'll get it up later today!Edit: And here it is! Just the novels, and one or two of these might be debatable if he's Listening or just eavsdropping. Also note that some of these moments he essentially gets nothing from it.
SF: Before the meeting w Bianca, eavesdropping on the guards; (debatable if Listening or not) outside his office, when Murphy's been stung; (as above) at Sells lakehouse - 1-3 times
FM: In the warehouse when he first sees the Alphas; in the Full Moon Garage (first visit); On McFinn's grounds before he's arrested; Right after he's entered Marcones estate - 4 times
GP: - 0 times
SK: at Reuel's appartment; at Reuel's funeral; outside WalMart when he's getting the car - 3 times
DM: At the harbor (by the Etranger); the Carpenter house (before meeting Molly in the treehouse); at the auction ball - 3 times
BR: Inari on the phone w papa Raith; the attack on Mavra's Scurge - 2 times
DB: at Georgia's place after the "fight" with Cowl; at the Field Museum (Bartlesby's office); Li Xian & Corpsetaker at the Forensic Institute; Corpsetaker at Bock's; before leaving the appartment after the zombie attack; Field Museum when looking for the Word - 6 times
PG: at Pell's theatre - 1 time
WN: Thomas' appartment (the guard and the cop); Raith Deeps (Vitto/Madrigal) - 2 times
SmF: - 0 times
TC: in LaFortiers chambers (Merlin/LtW) - 1 time
C: after running in to the Rampire in the jungle - 1 time
GS: - 0 times
CD: just for a moment in the fight with Fix, before consulting Intellectus - 1 time
Gate of Blood (Nick/Deirdre); fighting/fleeing from the Genoskwa
- 2 times
For a total of 27-29 times, spread over 12 of the 15 novels. Doing the short stories will be another time