I have used sweetened condensed milk a lot in different deserts and pies, but today I wondered if boiling is needed, is it necessary?
The whole point of canning is to produce food that won't spoil. The only reason to boil canned food is if you think it was improperly canned, and if that's true, it may not be safe to eat even if boiled. Botulism bacteria, for example, will grow in many improperly canned foods, and it will not be completely destroyed by boiling, though most of the botulism toxin will. Some molds and bacteria can also produce persistent toxins that won't be destroyed adequately by boiling.
In general, if you're afraid to eat any canned food without boiling, I'd throw it out rather than eating it.
Also, I'm not certain if you were implying that you would boil food in the sealed can. I wouldn't recommend that. Boiling sealed cans is potentially dangerous (if not closely monitored); they can explode if not kept complete submerged.
Assuming your condensed milk is sealed and was canned properly, there is no reason to boil it, nor any other properly canned food.