I found a website linking to my website that has lost its pagerank due to a penalty (pagerank slap) and is now PR0. However when you search the website it still shows up fine on Google. Should I contact the owner to remove the link?
Did you naturally acquire this link? A website losing its PageRank can happen for a ton of different reasons such as simply losing links. If it's a relevant site and a link you naturally acquired, there is absolutely no reason to get it removed. Unless of course, the website is spammy.