Companies or organizations should provide you with a clear process through which you can get access to your data. The GDPR does not specify in which format your data should be made accessible to you, but requires that such format is “commonly used” and “machine readable”.
Note that if you are requesting data to exercise your right to data portability, this only applies to data you have provided to a company or organisations (on the basis of the contract or on the basis of your own consent). You can not request data portability from a third party. For example, you can not request your data which is collected by third party trackers (other companies that track you with cookies and other scripts) on a website.