Cant find sparkplug number of 250cc loncin motor can anyone tell me what plug it takes

With the forks compressed all the way down, and the springs removed, you can fill them 6 inches from the top. You will need to use a siphon or maybe a turkey baster to get the correct amount in each fork leg.

Make sure all the letters and numbers on the plugs are exactly the same some plugs numbers and letters vary but still work, the way they are different is charge and heat settings some bikes work some dont, also make sure you use a torque wrench when tightening your plugs u can never be safe enough!

turn off your fuel supply, remove the air cleaner, spray a shot of brake cleaner, or starting fluid into the carburetor air intake, then try to start it. If it fires you have a fuel problem, (not enough, or flooding) if you can't get it to fire, it's a spark problem.

The easiest way to tell is to wait until the engine is warm and then put the lever in the opposite position. If the engine struggles, it is in the "choke on" position.

I think you didn't tell us what vehicle you have

How was the no spark in cylinder decided

A wire can jump a spark to the motor & you can also
ruin an ignition module doing so, unless your working on
a car from 1960's

You can have spark but it can be weak

There are tools to use for that

Spark plugs actually fire from the engine to the
plugs
Electrons flow from your battery neg terminal thru
all metal & fluids first ,then return on wires

if it just revs up the the centrifical clutch needs to be changed but if it doesnt then the trans or the rear end might be jamed or even locked up.

Take the plug out and go to Home Depot. Buffalo Tools makes that unit and Home Depot is a seller

You need to use an NGK 7092 Spark plug or equivalent. Note this is a NAPA part number & may not work everywhere.
So to answer your question, No you can't use just any plug.