Final answer:
Observe for a skin rash as a prior assessment for adverse effects of cefazolin (Ancef) in a client with a known allergy to amoxicillin.
Step-by-step explanation:
The prior assessment for adverse effects of cefazolin (Ancef) should include observing for a skin rash. Since the client has a known allergy to amoxicillin, it is important to watch out for any signs of an allergic reaction when administering cefazolin. Skin rash is a common symptom of an allergic reaction and can help indicate if the client is experiencing an adverse effect from the medication.