The first level of information is Settings > About phone > tap on Android version
There will be different info there by device and Android version … will usually contain kernel version. Two things significant to current patch levels are
- Android security update
- Vendor security patch level.
The name (of this date) can vary by context but these are what is meant by Android SPL and Vendor SPL.
Fairphone 5 had its own Vendor SPL thread Vendor Security Patch Level (SPL) in Fairphone 5.