Train or RandstadRail
Both the train and the RandstadRail connect at The Hague Laan van NOI station. The RandstadRail includes lines 3 and 4 that connect The Hague with Zoetermeer, and the Erasmus line that connects The Hague with Rotterdam.
When you arrive at The Hague Laan van NOI station walk towards the Ministry of SZW. At the exit, turn left immediately and follow the path for 200 meters until you arrive at the Wilhelmina van Pruisenweg.
You can find the HSD Campus in the first silver colored building (named HeadQuarter) on your left hand.