Hi , and welcome,
selepeed/ speedgear?,
of conventional gearbox?,
normally you'll have a allen key HEX plug on the front vertical edge of the gearbox,
park the car on level ground - then carefuly remove this plug,
the LEVEL is supposed to be so oil dribbles out - BUT I tend to find it wll have leaked a little oil over time..,
I use the allen key as a "dipstick" to see how much lower than the hole the ACTUAL oil level is,
if it's lower than a Centimetre , then you should really top it up/ changing the oil may be better if you've got doubts,
Charlie