score:2
The closest is the bus line Karlovac-Topusko. This passes VojniΔ (where the only access road to the monument starts) and continues along the road to the north of the monument. A stop like Biljeg looks like a good starting point for a hike. To the best of my knowledge there is no bus on the road leading up to the monument. You could try to hitch a ride up there from VojniΔ or take a taxi if you want to avoid the hike.
You can find the bus schedule on BalkanViator. Every day there are many buses on that line.