As many as you need. There is no limitation on the number of questions you can have in your survey. But keep in mind if you plan to ask the survey periodically, having many questions can negatively impact the response rate.
Note that there is a limit on the number of questions you can have in a given survey page, and the length of the content for each question. These two limits are placed to make sure each survey page is responsive and easy to navigate on all smartphones, even older and slower devices. If you add too many questions (generally more than 10) in a given page, it might impact the page's responsiveness for certain devices.