Let's start from the very beginning...a very good place to start :)

As TKT KAL is a Cambridge exam I think it's a good idea to take advantage of all the resources that their website offers.

The TKT KAL Handbook for teachers is available at
http://www.cambridgeesol.org/assets/pdf/exams/tkt/kal-handbook.pdf

This is the introduction to KAL you will find there:

Introduction to TKT: Knowledge about Language - a test of professional knowledge for English Language teachers

TKT: Knowledge about Language is an extension module of the Teaching Knowledge Test (TKT). It tests knowledge about the systems of the English language that aid a teacher in planning and delivering their lessons. The systems referred to are:

• Lexis
• Phonology
• Grammar
• Discourse

seen from the perspective of a teacher's language knowledge needs.