When you are discussing arithmetic, you can say
"Does 2+3 equal 5?" or "What is 2+3?"
In a context where you are discussing some specific object, say cookies, you can also say
"How many is 2+3?" or. "How many would 2+3 be?"
In a context where you are discussing some continuous ("not countable") quantity like money, you could also say
"How much would $2 + $3 be?"