i am familiar with getting camera position in world.(x,y,z) but getting (i,j,k) vector based on mouse click evades me. trying to be able to click on an arbitrary point on a sphere defined with a center and a radius. the math to find out if a vector intersects exists, as does the formula for finding the vector/sphere intersect point(s). (point closest to camera can be determined by selecting the point with least distance to the camera using the 3d distance formula)

problem is that i can’t figure out how to get the vector from a mouse click to fill in the blanks of the equations to complete my task. any help would be greatly appreciated.