JTAG 20-pin only 1 has data
You can't use a scope or logic analyzer to look for JTAG interfaces. First, most of the pins are input pins, so you won't see anything on those pins electrically besides pull-up resistors. And you won't see anything on the output pins if the interface isn't being actively used, and in the vast majority of cases the interface is not used at all except maybe in the factory. To find jtag interfaces, you need to do some sort of active probing. Either take a guess at the pinout and try to enumerate the chain, or use some sort of active search. I think there might be arduino code or similar that can automate this. If you go that route, make sure to use proper protection and level translation circuitry.