3GPP 24.501 v20.0.0 — the document's own text
8.3.2.11 DNN
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
The IE shall be included in the message when the PDU session is a non-emergency PDU session and the UE is not registered for onboarding services in SNPN.