If you change the reference sets of each part to "entire part", you'll be able to pick anything in the part for constraints. However, the "entire part" reference set brings a lot of clutter with it; when there are "helper" objects in the parts that I want to constrain to (but not always see in the assembly), I like to create a "constraint" reference set that contains the main body and any supporting objects to use in constraints. In the assembly, switch the component to the "constraint" reference set and create the constraints. When finished with the constraints, change back to the "model" reference set to clean up the display.
If I understand correctly you can see the CSYS'es but not select them to create your constraints? I suggest to check what layer settings you have. I believe that your referencesystems are on layer set to Visible Only. Check what layer your CSYS'es are on and change that layer to. Ensure that the layer where your Datum's reside is Selectable by having the checkbox active (red tick in the box), and ensure that the Visible Only is toggeled off (no tick in the Visible Only column)
Hi there Kapilsharma:
No I did not use NX for my renderings. I use the application from SAP called Riight Hemispheres Deep Exploration.