Quick, what's the hex code for question mark? How about the ampersand? Since, like me, you probably don't waste valuable space in your brain with that type of information, I have a little trick for you to quickly look up the hex encoding (or URLEncoding) for a character that doesn't require you building an ASP or ASP.NET page and calling Server.UrlEncode().
Go to Google and type the character in the search box and then click "Google Search". Now look in your address bar at the very end. Everything after the "q=" is the encoding of your character. For example, if I search on "?" I get:
Thus the hex encoding for ? is %3F.