Replacing whole milk with sweetened condensed milk for cheescake
Sweetened condensed milk is approximately 40% sugar, so you would need not quite double the sweetened condensed milk, and you would have to deduct the additional sugar from the recipe.

You would need to multiply the amount of milk by about 1.7 to get the amount of sweetened condensed milk, and then deduct 40% of that (by weight) from the sugar in your recipe (you can assume that sugar is  7 ounces to the cup).

The thing is, sweetened condensed milk may have a cooked down taste, so you may not get the same pure creamy flavor that you would from fresh milk.

If you have additional cream or half and half in excess of what is called from in the recipe,while it may make the cake somewhat richer, you may have a better outcome using that in lieu of the milk.  You also will not have to adjust the sugar if you go that route.