If you do a search for a site in Ranking Research and very few or no results are returned, there are typically two potential causes. But before we get into those, it's always good to verify the most obvious possibilities:
Have you spelled the site's URL correctly? Does the screenshot match the expected website?
Have you selected the most appropriate country and search engine?
Is the correct site scope selected (e.g. root domain / subdomain / subfolder / URL)?
Now that we've verified that isn't the problem, it's likely due to one or more of the following:
Insufficient data for the website
When looking up a site in Ranking Research, you're searching through the database of keyword rankings we've already collected. Only the keywords that are in our database will be shown in search results.
Our ranking database contains hundreds of millions of keywords, but due to the limitless possibilities of keywords, it cannot contain all possible keywords a site may be ranking for. If the site is ranking in a very specific niche or targeting very long tail keywords with low search volumes, it may be possible that many of these keywords may be missing in our database. You may still be getting organic traffic from these keywords, but they will not show in Ranking Research.
Important reminder: Ranking Research is most useful for sites other than your own (such as competitors). For your own site, webmaster tools such as Google Search Console will show you the keywords you're getting clicks and impressions from, which may be even better than data available in Ranking Research. In the Google Search Console Ranking report in Dragon Metrics, you can see the top 50,000 keywords per campaign updated daily (does not count towards your keyword credit quota). While this report is amazing for your own site, it cannot provide any data for competitors, which is where the true value of Ranking Research comes in.
Low SEO visibility
Another possibility is that the site is not ranking in the top 100 results for many keywords. If this is the case, the data on Ranking Research will be very limited. You can confirm this by looking at webmaster tools (such as Google Search Console Ranking) if it's a site you own, or by tracking rankings in Campaigns if you do not own this site.