the 'tell tale' - bit where the water should come out, is under the bottom plate of the main engine powerhead - underneath the bit the hood fits on
If there's no water coming out, don't run the engine! There's an impellor in the bottom of the leg where the gearbox/prop is that pumps water up the leg and around the engine. if the water pump isn't working, you'll seize the engine
it is possible that the exit of the tell tale may be blocked, bits of salt/crud etc, with the hood off you should find a small rubber hose that goes from the engine block to the bottom cover plate, that the tell tell hose, pull it off check its not blocked
if you're running the motor in a tub of water, makes sure the water level is well above the top plate on the gearbox, so the inlet for the water pump is fully submerged
if you've done all the above and you turnit over and there's still no water coming out, stop the engine immediately and don't run it again
you either need a new impellor in the pump, or depending on the model, there may be a thermostat on the head that is blocked
either way, don't run the engine till you've checked both out, or you'll seize the thing permanently at worst, or at best score the barrels/pistons so badly it'll be pretty useless anyway
impellors are cheap enough, 10 or 15 quid for something that size, and fitting is not a big job to do yourself, a dealer service will probably be 50 or 60 quid for something that size, which will include and impellor change