I would like to know more about Impressions in twitter. How to get particular account’s or user’s impression using public API?
Nothing on impressions in Public Stream or REST APIs unfortunately. I don’t know much about the Ads APIs, but maybe the new Gnip thing might be worth looking into: https://blog.twitter.com/2016/gnips-audience-api-is-now-generally-available
Any third party access to measure impressions. As GNIP is quite costly to use.