Is Jitsi or WebRTC support Scalable Video Coding (SVC)
VP9 is not Scalable Video Coding.
What do you mean? VP9 uses SVC to handle the layers. It’s the equivalent of simulcast on VP8.
There are 2 types of SVC: temporal and spatial. Are you asking about one of them in particular?
No, actually there are three components of SVC: Temporal, Spatial and Quality. All three are implemented in Scalable Video Coding which is an extension of H.264. I think SVC is not implemented in Jitsi but I am not sure.
Jitsi does not currently implement SVC for H.264, in large part because last I checked none of the browsers implement it either.