A new edition of Practical Transformation Using XSLT and XPath by Ken Holman is out.
While not topic map specific, ;-), this is one of the two resources you need for transformations getting to (or from) topic maps using XSLT and XPath. The other one, would be: XSLT 2.0 and XPath 2.0: programmer’s reference. (You can also use both of these for non-topic map, XML based work.)
While your looking at Ken’s training resources, note his series on UBL (Universal Business Language).
I mention that because the greater the exposure of business systems the greater the need for the mapping of semantics (that means topic maps).