how do I get current HRV

[TiggerPooh]

What is the most feasible way to get current HRV for user, whether I show the data on the Fitbit display or the Fitbit iOS app, or my own iOS app, if possible?

[Gondwana]

I gather, from your other post, that you're using an Inspire. Inspire can't use the SDK, so you'll need to use the Web API. Note that real-time ('current') data can't be obtained from the Web API.