Not set
The ‘keyword’ (not set) simply identifies traffic that doesn’t arrive via a particular keyword and hence may not come via any search at all. This includes traffic coming from email, referral sites, or even things like Google Images. The latter might be confusing, but it helps to know that visitors coming from Google Images and Google Maps are classified under referrals with the source google.com, not organic search. Because keywords are automatically set for search traffic, the (not set) keyword will never appear in your organic Search reports, so it is likely something you won’t have to worry about. Don’t consider this one in light of keyword performance!
Source: http://www.gravitatedesign.com/blog/not-set-not-provided-mean-google-analytics/
Not set
The ‘keyword’ (not set) simply identifies traffic that doesn’t arrive via a particular keyword and hence may not come via any search at all. This includes traffic coming from email, referral sites, or even things like Google Images. The latter might be confusing, but it helps to know that visitors coming from Google Images and Google Maps are classified under referrals with the source google.com, not organic search. Because keywords are automatically set for search traffic, the (not set) keyword will never appear in your organic Search reports, so it is likely something you won’t have to worry about. Don’t consider this one in light of keyword performance!
Source: http://www.whereoware.com/blog/not-set-vs-not-provided/2013/05/
This is in Acquisition, Campaigns, Organic keywords. If you're talking Acquisition, SearchEngineOptimization, Queries - this works different, see text in below.
So - in general Analytics can't figure keyword there. But this is not how GA should work. You should tracks your KWs in Google SearchConsole. There is "SearchTraffic" -> "Search Analytics" with all impressions, clicks, ctr and positions. There you can make report for web, image or videos. You can split traffic by countries, pages, devices (desktop, tablet, mobile) and much more. Here is link:
https://www.google.com/webmasters/tools/search-analytics?hl=en
but there you must add your site and verify it.