As far as I know: If they invite you, that's already half the rent. There will be some talk with managers and pilots and a sim ride. They also might check your license and log book very carefully, depending where you are from.
In the sim you do a few approaches but ILS, one OEI, GA and RTO. Either on a A320 or a A300, depending on availability.
These information are only second hand. I never applied for SLK. Generally all airlines in SIN do it the same way.
Dani