From Teflpedia

TKT are the initials for the Teaching Knowledge Test. It is one of the University of Cambridge TEFL Qualifications.

The test ensures that teachers have a strong foundation in the core areas of teaching knowledge needed in the English language teaching classroom. The University suggests that, after taking TKT, teachers who want to develop their knowledge go on to other well-established teaching awards, such as ICELT and CELTA.

Full information can be obtained at the University's website here.