I am working with "crafting a bomb" in D&D 5e, and was just wondering if, in the D&D world Sonic Damage encompassed the effect of a concussion blast or if it was considered something else. I don't know where to look for anything definitive.
Now that the official PHB is out, you can find the complete list of Damage Types on page 196.
Sonic would be what is called Thunder.
The definition actually makes use of the word Concussive:
Thunder. A concussive burst of sound, such as the effect of the thunderwave spell, deals thunder damage.
If the type of bomb you are referencing is what we have in our world, there can be three types of damages:
People really close (maybe 5 ft or less) may be hurt by the deflagration, which is Fire damage burning the powder used to explode the bomb; for a small bomb, such as a grenade, this damage would probably not be that much (in D&D terms at least), because it burns really quickly and is very small, albeit quite intense.
People further are likely to be hurt by fragments flying really fast, those can be viewed as either Piercing (glass, metal) or Bludgeoning (rock); this goes further than the deflagration to around 60 ft for a modern bomb the size of a grenade; you could also have half damage up to 120 ft for left over fragments...
And people yet further away would only be hurt by the sonic wave assuming the bomb was large enough; that one would be the Thunder damage I mentioned above.
All of that very much depends on how the bomb is built. Today we also build concussion grenades that kill people within 6 to 7 feet of the explosion. These do not have much fragmentation damage. They build those with more explosive in a thinner container. Also expected to be used to kill someone close to the explosion, bit of the grenade can often be found 200 meters away. So there are still possible fragmentation damages (up to 600 ft). These could have quite high Thunder damage.
As a complement, I found out that there is information about explosives, such as bombs and grenades, in the DMG p. 267/268. It does not really talk about concussion grenade though, only fragmentation.