Que1Can viruses respire. If yes how they respire when they are inactive, floating in air or settled on the door knob they are non living and non living thing donot respire and respiration neccessary for survival

No it is not necessary. Respiration is not ther only condition necessary for survival. There are other conditions like growth, reproduction etc. also.

Virus is an entity that carries its own genetic material. But it needs a suitable environment, a living host to activate it. Then it reproduces or starts multiplying in the living host.

That is why virus is considered as a border line between living and non-living.