If the Apple Store performed a clean install of Mojave (wiping the drive beforehand), then Pages, Numbers, and Keynote are gone from the drive — because they are not installed by the operating system.
Apple only provides the most current, full installer of its applications in the Mac App Store, and (presently) the versions of Pages, Numbers, and Keynote (all v10.2) require a Catalina 10.15.7 upgrade before they can be installed. If you performed a Time Machine backup prior to the Apple Store, then you have the means to restore the Mojave compatible versions of these applications by launching Time Machine from your Applications folder and selectively restoring the applications.
Without a Time Machine backup, and in my own testing, by removing Pages v10.1 from my Mojave 10.14.6 installation, the Mac App Store refused to replace it, and I had to use Time Machine Restore to retrieve it from my hourly backups. Historically, the Mac App Store would inform the obvious, that the version in the store is incompatible, and then offer to replace the missing version of the application with the most recent compatible for your operating system. It did not do that for me on Mojave.
With respect to the last paragraph, you can launch the Mac App Store, sign-in with the same Apple ID that was used to install Pages, Numbers, and Keynote previously, and then press command-0 (zero). This brings up the previous purchases panel, and then click on the Pages, Numbers, and Keynote buttons to see what happens. Maybe it will replace them, or not.
