The documentation is a bit unclear, but I believe it is 12VDC without a need for pull-up resistor.
I suppose the easiest way is to directly control the input to the SSR using your open collector output. Just connect the open collector to the negative input to the SSR, and the SSR’s positive input to 12 VDC. The ground side of the 12 VDC should be the same as the ground side of your open collector output.