I've got a 2007 Yukon XL Denali, and my bulb spec. for the bottom of the side view mirrors is: Wagner 17177, Philips 12961, GE/ACDelco W5W, OEM 9442399. I'm not sure if the 07 Burb light bulb specs. are the same as the 07 Denali light bulb specs, but I would suspect that most would be the same.
KB and Double are correct, in that this is the same bulb sped used in the license plate and corner marker lights.
I identified the light bulb specs of all of the lights on my 07 Denali, as well as mapped to the appropriate JDM Astar LED replacement part numbers in the thread listed below, if that would be helpful to you.
https://www.tahoeyukonforum.com/threads/time-for-new-headlight-assembly.108917/#post-1300984 Post #8.