If I read your question correctly, you want the data card of a part to show the assembly it is used in, and have this value added automatically by the process of creating the reference in the assembly.
If that's correct, I think you would need a custom add-in to find the reference to the part and then add that part number to the variable shown in the data card. If this was done as an add-in for SW (rather than an EPDM add-in) you might possibly be able to have the variable update occur when the part is inserted in the assembly. It seems it would be rather complicated, though, and potentially quite expensive.
As Brain Said,Youi will require a custom addin for this.
I was wondering wat will be the case if the part is used in the sub assembly?
If You setup allows only one assemblt per project and rest all are part.the ni think we can have a work around.