Can one say this phrase as πώς δείχνεται σεβασμό;? (with a passive verb?) As jeanprendiville explains, in English "How do you... (do something)?" usually means "How does one... (do something)?" (not literally "YOU").
It's the same in Greek. Πώς κάνεις (κάτι) is also most of the times impersonal and does not literally mean "you". Πώς δείχνεται ο σεβασμός (nominative case, because it is the subject of the sentence) means the same thing, but it's a different syntactic structure.