I can't really help with Sentinel becaue I have never used it.
TRS is Trunked Radio System.
Grand Forks AFB frequencies are not in the database. I couldn't find any on the state or county pages.
Most of the air traffic control frequencies can be found at:
Flight Service
You will most likely have to search the aircraft bands and find the military aircraft non-ATC frequencies yourself.
The base public safety and support services are probably on Site 1-10 of this nationwide USAF P25 trunked radio system:
United States Air Force (157) Trunking System Profile
www.radioreference.com
There is only one talkgroup ID listed for Grand Forks AFB. A base that size probably has 100 or more of them. You will have to search and find them yourself. There is a chance that some talkgroups are encrypted. If so you will not be able to receive them.
There is another older Motorola Type II trunked system in the database:
Grand Forks Air Force Base Trunking System Profile
www.radioreference.com
This system was probably converted to P25 (the USAF 157 system above) and probably no longer exists.