If you never installed Pages from the Mac App Store since Oct 2013, then there is no means to get Pages compatible with macOS Mojave now. You will either need to use Pages for iCloud, or another word processing product that is compatible with Mojave.
Contrary to the first paragraph, if you did install Pages from the Mac App Store with your Apple ID since Oct 2013, then launch the Mac App Store on Mojave and sign in with that same Apple ID. Press cmd+0 (zero) in the Mac App Store to open the Purchases panel and if Pages is shown there, select it and do not click Cancel to any dialog that may appear afterward. This should get you the last compatible version of Pages for Mojave 10.14.6.