If you look at the aircraft registrations for the flights departing JNB to DOH over the last week, one sometimes two of the three daily flights have had Q-Suites.

QR1363/QR1364 2 out of 7 flights in last week were Q-Suites
QR1365/QR1366 3 out of 7 flights in last week were Q-Suites
QR1367/QR1368 or QR1477/QR1478 2 of 7 flights last week were in Q-Suites

so 33% chance based on last week.