In the code num_var = "fifteen", what is the data type of the value?

I think the data type is a string. In computer programming, a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable. The latter may allow its elements to be mutated and the length changed, or it may be fixed (after creation).

The Data type is clearly a string because you put it in quotation marks, this tells the computer its a not a integer, but a readable "String"