"There is probably no one in Russia who wouldn’t know about it." or "There probably isn't anyone in Russia who wouldn’t know about it."

Very good job!

Your sentence is Grammatically correct ! It is just better to put a comma after ''probably'' to make it more stronger because it sounds as a standout word that attracts the attention of a reader. You use ''would'' which means that you are not sure about whether Russians know or not about that unidentified thing you are referring to.Therefore, ''Would'' is very suitable as it backs up the previous mentioned word '' probably''. Reader will figures it out from the very beginning that you are not giving a fact that is true 100 per cent, rather you are doing a kind of your own deduction :)