Yes, you're right, the "title" attribute is the one to use for an HTML tool-tip. But I don't understand the rest of the question. What's a "field" in an XML document? And why do you say "dynamically"? Perhaps an example of your XML and what you have so far in your XSLT would help.
Q. How to ask an XSLT question? A: The easiest way to get answer real quick is post the original xml source, then post what you want to get the xml/html result. Of course, make it simple, and illustrate the point you want to solve only. Then your own approach which does not work as you desired. Many brain exercisers will solve your problem quickly. The answer will help others too.