In primavera P6, how can you add the scope of quantity to the individual activities?

The item you should look for is Budgeted Quantity .

1st u need to add resources , then to assign to each activity their resources , after u just click on the activity in the table below u ll find resources tab , click on it , now u can add the quantity of each resource for each activity

Firstly before you assign resources to your activity ,you have to make bill of quantity of your project by using Exel program from which you can define the amount of the labor , non labor and the materials.
After you assign a resource to your activity ,you can use the resource tab in the activity detail section to apply the budgeted units of your resource and then click schedule that is all.
.

You can open a custom column and feed our bill of qty

First you need to add all the scope as resource (e.g for concrete you need to add concrete as a material resource, labor for placing concrete as labor resource and equpiment use in the placement of concrete as non labor resource) and then assign the scope of each item on there respective resources in the resource tab under budgeted units.