Best placed in September. It is deep in the southern sky and never rises for most of the northern hemisphere.
Mensa is centred near right ascension 5.5 hours, declination -80°. It is deep in the southern sky and never rises for most of the northern hemisphere.
It reaches its highest point in the sky around local midnight in September, which is when it is easiest to pick out. Earlier in the year it rises before dawn; later, it is already setting in the evening.
SkyRef draws Mensa in its real position for wherever you are, right now, along with the other 88 IAU figures.