3GPP 24.501 v20.0.0 — the document's own text
8.2.19.34 NSAG information
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
If the UE has set the NSAG bit to "NSAG supported" in the 5GMM capability IE of the REGISTRATION REQUEST message and the CONFIGURATION UPDATE COMMAND message is sent over 3GPP access, the network may include this IE to provide NSAG information to the UE.