The GDPR component by default is integrated with the core Joomla! components for users and contacts management as well as with a series of common extensions such as RS Forms Pro, Chronoforms, JomSocial, EasySocial, etc in order to:

• Show the privacy policy checkbox in the registration form if any
• Show buttons to delete and export a user profile if any

If you don't see the privacy policy checkbox appearing on a third-party extension form, you should firstly check if the extension that you need to integrate is included in the extensions list and if it's enabled.

If that's not the case probably you are using a module to include a form, the component.viewname is not matching with the default one included in the standard integration or the extension is not integrated at all, so there are 3 ways to integrate the privacy policy checkbox with a third-party extension that shows a form using the configuration settings shown in the image below:
1. Specifying the view name used by the component to show a form and a CSS selector to match the form
2. Specifying the form name and the form task used by the component to show a form
3. Simply using a dynamic checkbox and copy/paste the placeholder wherever you want the checkbox to appear (see PDF docs at the paragraph 'Dynamic checkbox')

Refer to the PDF docs at the paragraph 'Integration with third-party extensions' for detailed explanations about this kind of configuration.

To easily find the component.viewname, form name, etc used for a certain menu item, it's recommended to enable the 'Debug mode' parameter under the advanced configuration of the GDPR component so that informative labels will be visible on the page. As an alternative you can check the raw link included in the Joomla! backend for a given menu item or to temporary disable the SEF URLs in the Joomla! global configuration and check the website frontend.

Take care that if you are using a Joomla! module to embed a form into your pages, for example from a third-party extension having a related module to display forms, you can't specify a view name for the component associated to that form and the standard integration could not be enough. Indeed a module may appear on any page of your website, based on menu assignments, so several components/views may be executed everytime that the module containing the form is displayed.
In this case you have not to specify the value 'com_xxx.viewname' of the component itself that generates the form, but the value 'com_xxx.viewname' of the component executed on each page in which the module including the form is displayed.
Let's say you have a Chronoforms module including a form shown in a Joomla! single article page, in this case you must specify in the parameter 'View name for custom components' the value 'com_content.article' that relates to the component and view used on that page.

As an alternative consider to use the 'dynamic checkbox' feature, in such case you can simply copy/paste the dynamic checkbox placeholder wherever you want for example in the contents rendered inside a module. Additionally if your form already includes a checkbox for the privacy, you can just reuse it instead of adding a new one and at the same time take advantage of the tracking system provided by the GDPR component and based on the 'Logs of user consents', for more informations refer to the PDF docs.