The link tells you how to check the level -- well sort of. It is more focussed on changing the ATF and then getting the level right.
To just check the level:- Have the car level. Start the engine and get the gearbox fluid up to the correct temperature (45degC). This can be measured on the iCarsoft i980 (and probably other OBD tools) or using a infrared temp gun on the gearbox sump (less accurate).
With the engine running, remove the sump plug. The ATF should just splutter out if the level is correct. If it comes out in a big flow there is too much. Let it out until the flow reduces to a splutter and then replace the sump plug.
If none comes out then the level is too low.
Note:- the ATF temp is correct for a sump with the green stand pipe -- but of course you won't know what colour stand pipe until the sump is dropped !!
I suggest that you need a plan for what to do if the level is too low which is probably the most likely scenario. To get more ATF in you need an adaptor and a pump (plus the correct new ATF). Then how much to pump in? Then is it worth pumping in new fluid on top of old fluid?
Do you suspect that you have an issue?
If so, just get the ATF changed (or DIY it) using new filter & sump gasket, the correct spec ATF, new sump bolts, maybe new TC drain plug, sump bolt gasket.
2015 w204 c class amg sport premium +65 ford kuga 2.0 cdi zetec awd..
if it aint broke and all that . but to find the level , have it renewed then you know its all good. i certainly wouldnt be removing the sump bung , any lost fluid cant be put back in , not by the diyer anyways.