ZAK (Zoom access token): This can be retrieved through the REST API and is specific to the user you are retrieving it for. See our documentation on the user token endpoint here and feel free to reach out over on #zoom-api if you need any assistance using the API.
User ID: This is a unique identifier generated for a user when they join the meeting. Depending on what you are using this for, the method of retrieving may vary. Could you provide some context on when/where you are trying to utilize this field so that I may better advise you?