From GameWatcher: “Emissary Standing is currently one of the most desirable resources in Warframe, due to it being useful for upgrading your Nightwave Season 2 rank and level, which in turn unlocks exclusive rewards.
There aren’t all that many ways to get Emissary Standing, and the good news is that it’s not too difficult to farm, either. For ease of access, we’ve decided to bundle those together and explain them all in one fell swoop.”
Source: N4G PC Warframe Emissary Standing – How to get it?