How do you know you are looking at a locomotive with DCC if you have no paperwork to refer to?
What locomotive do you have?
I check to see if a locomotive has a working decoder by trying to read back some CVs. If I suspect it has a decoder that does not support reading back, I attempt to program CV01 to 03 and CV29 to 00. Then I try to run the locomotive on address 03 using 14 speed steps. If it runs, it has a working decoder. If it does not, it has not.
If you can tell us what the wheel arrangement is, we can probably tell you if it's DCC or not. Or refer to the Products section of this website.