Regardless of the booking source: tk.com, OTA, Corporate Travel Agency it should be exposed to you during the booking process. It might be hidden or might require clicking, but it is somewhere there. These rules are very long and written in a very confusing way, but you need to look for Categories and 31. Cat 16 is written in plain language, Cat 31 is machine readable - thus more complicated to understand.

If you have not downloaded these rules during the original booking process, you need tools like Expert Flyer or GDS to retrieve them.