It "SHOULD" be right behind the utility panel. There is a 12X12 wood panel that probably needs to be removed in the storage compartment that will allow access to the filter. Your dealer was "SUPPOSED to show you all that when you did your walk through.
PINNACLE 2015 38FLSA. aka: "Roam Sweet Home"
The online manual for the 2016 Jayco Seismec makes it look like an option. Its says under
Sanitizing Instructions, Full System Canister water filter (if so equipped). Maybe check your build sheet and see if it is listed, if not you don't have one.