In your .pro file: INCLUDEPATH += C:\Users\moh\Downloads\qxmpp-master - if this directory contains a directory named "qxmpp". If that isn't the right directory, then find the one under qxampp-master that contains the "qxmpp" subdirectory. That's the one you want.
According to your screen shot there is am "src" directory. Maybe there's an "include" directory as well?
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