It all varies from track to track to be honest, on Silverstone I was advised to add pressure to reinforce the side walls on the long high speed bends. At Cadwell it was better to drop pressure as the constant direction change and generally low speed means the tyres heat up quick.
And where do I get this info? Simples, find an instructor or event organiser, they're always only too happy to share their wisdom!
Back to original question, look in your supplementary RS handbook it has recommended track tyre pressures in there, can't remember the values.