Final answer:
The nurse should immediately report the client's high temperature of 39.4° C (102.9° F) as it may indicate neuroleptic malignant syndrome, a serious condition associated with antipsychotic drugs.
Step-by-step explanation:
The priority for a nurse to report to a provider for a client taking chlorpromazine with a diagnosis of schizophrenia would be a temperature of 39.4° C (102.9° F). This could indicate the presence of neuroleptic malignant syndrome (NMS), a potentially life-threatening condition associated with the use of antipsychotic medications. While headache, constipation, and dry mouth are common side effects of chlorpromazine, they do not typically pose an immediate threat to the client's health. In contrast, the high fever is an urgent symptom that requires prompt medical attention to prevent serious complications.