In general adamantine weapons always deal critical damage on a hit:
Whenever an adamantine weapon or piece of ammunition hits an object, the hit is a critical hit.
- Xanathar's Guide to Everything, page 78.
However, in SKT chapter 6 room 14 (page 154) it says:
She wields an adamantine greatclub. This magic weapon has no bonus to attack or damage rolls.
Does this mean it also does not crit? Or does it still crit like adamantine weapons do in general, but simply has no +n to attack or damage roll?
Also: is this a property of this particular weapon in this adventure? Or is it a property that always applies to adamantine greatclubs?
Outside of D&D lore this would make sense because adamantine is a very light material but is still very strong and can be sharpened. This makes is a great material for piercing and slashing weapons (swords, axes, arrows), but a terrible material for bludgeoning damage. However, I don't know if this applies in D&D lore as well (I haven't read it anywhere up untill now).