I have something like that too in mine, but it's not filled out completely. This owners manual is for everything (looks like they just slapped a "Coachmen" cover on it). At least it's something. There was also a hardcopy with the coach.
We change our oil every ~60 hours. Last oil change was at 144.5 hrs; next one sched for ~210 hrs.
Here are some of those generator specs too if you also have this model (I had gotten these from another forum). I wanted to get a handful of spare parts to have just in case, which I got from Camping World.
Onan 5500 RVQG gas generator
SAE 15W40 (we use this one "OnaMax")
Oil Filter Onan#122-0836
Subs: Napa FIL 7398
Oil filter removal tool Onan# 420-0577
Oil Capacity 2 qts
ELEMENT-AIR CLNR Onan#140-3116
Subs: Wix 49087
SPARK PLUG Onan#167-1638 Takes 2
Subs: NGK BPR4EY
FILTER-FUEL at fuel pmp Onan#149-2341-01
Note: Filter at carb no longer used. Use Onan Kit A029S253 to replace
Here's what I have for the water filter, too:
Hydro Life HL200 Series
Cartridge – C2063