Final answer:
The nurse should have the spouse perform the procedure and observe as it is being performed.
Step-by-step explanation:
To determine if the spouse understands the procedure of changing the client's colostomy bag, the nurse should have the spouse perform the procedure and observe as it is being performed. This allows the nurse to assess the spouse's comprehension and ability to perform the task correctly. Asking if the spouse has any questions, if they understand what items are needed for the procedure, and if they feel comfortable performing the procedure are also important, but actually observing the spouse performing the procedure provides the clearest indication of understanding.