Exactly how much Tnt do you need to destroy the asian continent
I'll assume "destroy" means "apply force sufficient to kill all humans and turn any human made structures into rubble".
Even though most of Asia is uninhabited and unpopulated, I'm also going to apply this to the entire surface area of Asia anyway because the question is about destroying Asia not the people and things they built on Asia. That's 44,579,000 km2.
If we used one giant bomb it would be extremely inefficient. Much of the explosive energy will simply go up in to the air. Instead, a large number of smaller bombs distributed around the continent will be much more efficient. How you do that is not my department.
For example, the overpressure necessary to destroy most buildings is about 36kPa. A 1 kT (kiloton) airburst will do this out to about 0.7km in radius or an area of 1.5 km2. A 100 kT bomb goes out to 3.2 km or an area of about 32 km 2. A 100 fold increase in bomb size yielded only a 21x increase in area destroyed.
From there it's simple math. If a 1 kT airburst will destroy 1.5 km2 then you need about 30,000,000 of them to destroy the 44,579,000 km2 of Asia or the equivalent of 30 gigatons of TNT.
The entire world arsenal of active nuclear weapons could not do this. We have maybe 1 gigaton of explosive power, but they're mostly in the 100 kT range and so would be significantly less efficient.