there isn't any node inside volume vop to create or set attributes. how can I do that?

Use parameter VOP (for creating and setting attributes), and connect your data to it input.Set export flag to always.

You cannot create Attributes in Volume VOP
Every attribute is a volume primitive or 3 primitives (for vector), it will not get created when you export parameter from Volume VOP, it needs to exist before

so first create empty (or any) volume primitives you need with correct names (especially for vector primitives, they should be called name.x, name.y, name.z, Volume SOP does that for you)
then you can access them in Volume VOP as Alex said and they will be read and written correctly

Yeah sorry, my bad. Attributes should exist in volume :roll:

thank you for your answers but name only use primitive and point as category. what happened if I want to get or set detail attributes. I want to attach a number to a volume. I think the best way is using detail attributes but with this approach how can I set this kind of attributes.