It's an incredibly vague (and basically unanswerable question). "The Jewish percentage in the 13th century" - percentage of what? Percentage of population, I suppose.

But then that raises another, equally important question - where are we talking about? A better question might be "What percentage of the English population was Jewish in the 13th century" That question would be answerable, as there is lots of information about English Jews in the 13th century.

That's probably why there are no answers.