I want to find top ranked keyword from my blog, it means I want the keyword that gives me first ranking on SERP.
Knowing that is worthless, by the way. You might be ranking number 1 for "best cat litter tray thats pink and fluffy", but if no one is searching for that term that it means nothing.
Please, stop trying to "do SEO" and just concentrate on writing worthwhile content.
Here are two sites that may help you: