If you started with a new document and did not save the content even once, then when you quit Pages, that Untitled.pages document would be permanently lost.
If you did save your Pages document once, and gave it a meaningful filename, then it would continue to autosave with your changes every 10 - 15 seconds. That document would survive your quitting Pages, and would also be on a Time Machine backup of your home directory on the startup drive.
If you remember the filename, you can launch Time Machine Restore from Dock : Launchpad : Other : Time Machine, and use the arrow to go back in time to just before you lost track of the file. If you find it, you can select it, and click Restore.
If you accidentally moved the folder containing the document, or the document itself to the Trash and emptied the Trash, then other than paragraph two, your document is gone, and unrecoverable.
If you have Spotlight active on your startup drive, and in System Preferences : Spotlight : Search Results : [√] Documents selected, then you should be able to locate the document with the following Spotlight search:
kind:pages AND name:"partial filename"
That quoted partial filename is only if there is white-space in the search string, otherwise you can enter a unique, unquoted partial name, and if it is on the startup drive, it will find it. Have you also looked in iCloud Drive : Pages folder?
