I've tagged one of my Disa photos with the relevant flower parts.
The pollinia are enveloped by those long whitish structures on the column. If you take a tooth pick and touch the viscidium you should be able to pull the pollinium out (it looks like a long yellow tassel). To pollinate the flower, place the pollinium on to the stigma. The receptive stigma is usually sticky enough for the pollinium to stick to but I prefer to attach the viscidium just above the stigma to ensure the pollinium stays in place (you may need another toothpick to help dislodge pollinium from the first toothpick). The pods develop quickly so keep an eye on the pods to make sure you don't lose the seed. I find seed production can be draining on Disa and I have lost smaller plants after pollinating them. I usually only pollinate large plants and preferably plants that I have a few divisions of.