Evernote is stored on your computer in the form of a local database file that contains all your notes and their associated data. This allows you to access your notes even without an internet connection. However, it's important to note that while your notes are stored locally, they are also synced to Evernote's servers in the cloud.
This means that if Evernote were to go out of business or change their business plan in a way that you can't continue using their service, you would still have access to your locally stored notes, but you might lose access to the cloud-based features and syncing. To ensure the safety of your data, it's a good practice to regularly export your notes as backup files, which you can store separately on your computer or in another cloud storage service.