How much space does 1kg of air occupy? the density of the air is 0.0013g/ml

First, convert the unit of kilograms into grams, since the density of air is in grams/mL,
1kg = 1000g

In simple language, what you want to find here is the number of mLs that can fit into the 1000g.
In other words, how many times of 0.0013g makes up 1000g.

The word "space" in the question is referring to volume.

Working:
1000g ÷ 0.0013g/mL = 769,231mL (rounded off to the nearest whole number) OR 769.231L OR 769L (rounded off to nearest 3 significant figures)

Hope this helps! :)

p.s. by the way, this sounds more like a Chemistry than a Biology question