There's no interface in either XSLT 1.0 or 2.0 that allows you to read a schema or DTD into your code at the semantics level. You can read the raw text, of course (or in the case of XML Schema, the raw XML), but it won't help you much unless you want to do an enormous amount of analysis of what you find.
What you can do in XSLT 2.0 is to specify that your output must be valid against a particular schema. The system won't magically create valid output for you, but it will tell you (often at compile time) if your code is generating invalid output.
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference