Hi Igor,
You can find osmo-msc specific CTRL commands in the User Manual section 6 "Control interface" : https://ftp.osmocom.org/docs/latest/osmomsc-usermanual.pdf
You should be able to similarly find available CTRL messages for other osmo-cni nodes in their User Manuals, available in same directory: https://ftp.osmocom.org/docs/latest/
Feel free to open tickets if you are interested in any kind of CTRL cmd which is not there yet, and/or submit patches implementing them.
For your information, if you want to interact with the CTRL interface you can find useful scripts in osmo-python-tests: https://git.osmocom.org/python/osmo-python-tests/tree/scripts/osmo_interact_...