There is no one answer.
Factors to consider is age of chameleon, type, gendre, how much access to outdoors sunlight it gets, and what insects you offer and what you feed the insects, and brand of supplements.
And as ryan said "One of the best ways to ensure chameleons are getting proper nutrition is through the foods they eat" - a variety of well gutloaded insects is key. For more info on feeder nutrition, see:
https://www.chameleonforums.com/blogs/sandrachameleon/75-feeder-nutrition.html
Many insects (such as crickets) have a poor calicum to phos ratio, hence the LIGHT calcium dusting.
Those raised 100% indoors might need a little help with D3 now and then, even though they have UVB emitting light tubes. Rep-Cal has 400,000 IU/kg of D3 whereas Miner-All (I) has 4,400 IU/kg of D3 and I think 150IU D3 in Nutribol (which i believe also has Vit A so be wary of using this very often). That's a considerable difference in D3 strength.
My supplementing schedule (for my panther chameleons) is much like that described by Chameleon97. I use a calcium (no phos or D3) lightly dusted on most crickets. I use calcium with vitamin D3 once every other week. I use a vitamin supplement (without preformed vitamin a) once every other week (the week opposite to D3). I rarely dust anything other than crickets, mealworms (which I dont offer often) and sometimes superworms. I almost never dust stick insects, moths, roaches, butterworms, cabbage loppers, isopods, etc. I pay attention to gutloading.
This blog entry has links to many previous threads and other websites with useful information regarding supplementing.