Here is the list of Q codes given in the IRTS syllabus, which is included in the same document as the Sample Paper. Presumably these are the ones you need to know, rather than learning a more exhaustive list:
QRK What is the readability of my signals?
QRM Are you being interfered with?
QRN Are you troubled by static?
QRO Shall I increase transmitter power?
QRP Shall I decrease transmitter power?
QRT Shall I stop sending?
QRZ Who is calling me?
QRV Are you ready?
QSB Are my signals fading?
QSL Can you acknowledge receipt?
QSO Can you communicate with ... direct?
QSY Shall I change to transmission on another frequency?
QRX When will you call again?
QTH What is your position in latitude and longitude (or according to any other indication)?