I think πώς δείχνει σεβασμό; should be accepted. It means how does one show respect, the third person rather than the second.
"How does one show respect?" I would say it: "Πώς δείχνει κανείς σεβασμό;" or "Πώς δείχνει κάποιος σεβασμό;". "Πώς δείχνει σεβασμό;" by itself alone wouldn't make sense, but it could be used when the subject has already been mentioned.
"Πώς δείχνεις σεβασμό;" has the meaning of "How does one show respect", too, like "How do you show respect?"