They don't have a "dip stick" as such.
The gear box is a sealed unit. If you haven't changed it for over 2-3 years drain it and the top it back up.
To drain do the following.
1, Jack car up
2,Remove the spedometer from the top of the box - this is really tricky and may require the air pipe to be removed.
3, Just like draining the engine oil there is a plug at the bottom of the gearbox . undo and drain. replace plug.
4, Unfortunately I'm at work now and can't remeber which gearbox oil you use but check the haynes. I use a 0.5Ltr bottle as it's small and has a long neck and IIRC it takes either 3 or 3.5 ltrs of oil.
5, once topped up refit the spedometer and job done.
However I think your thrus bearing maybe on it's way out. Some micra's clutches can some times give out after 30,000 miles (give or take).
Mine made a noise untill I dropped the clutch. 6 months later on a very steep hill my clutch gives up! lol