From my experience, do as much research as you see fit, make sure you include the basic company information, what their policies are, their goals SE by numbers (which is found on their website) as well as the rolling stock they use. They don’t expect you to know all the routes etc at this stage, all they see really looking for is the London terminals so as long as you know them you’ll be alright. What they do expect you to know inside and out is the TPWS sheet that they give you so make sure it’s firmly in your head! From my experience they don’t ask you about their depots but just incase you need to know I BELIEVE their depots/driver operations areas are as follows:
Ashford,
Ramsgate,
Dover,
Faversham,
Gillingham,
Dartford,
Slade Green,
Grove Park,
Hastings,
Tonbridge,
Orpington,
Victoria and Charing Cross
(If I’ve missed any then please can others correct me!)
my final bit of advice would be to scan through this forum, it’s been massively helpful and people have spoken about their experiences and everyone’s been a massive help!
Best of luck!