Final answer:
The health care practitioner proposing the treatment is responsible for determining a patient's capacity for consent under the Health Care Consent Act.
Step-by-step explanation:
Under the Health Care Consent Act (HCCA), the responsibility for determining capacity for consent to treatment rests with the health care practitioner who proposes the treatment. It is not the client, the substitute-decision-maker, nor the Public Guardian and Trustee (PGT) who has this responsibility. Although parents can provide consent on behalf of their children, this does not mean that children are inherently incompetent to provide consent. The capacity to consent can vary depending on age, maturity, and the nature of the treatment.