anchoring a moving graphic to a specific point in a video

Apologies in advance as I'm sure there is a proper, technical term for what I'm asking, but I simply don't know it! (feel free to educate me!)
I want to add a graphic to a video which is fixed/anchored to a certain point.
Specifically, I want to add a line or arrow that moves in relation to a moving object but stays anchored to a point in the clip which also moves.
https://torokhtiy.com/pages/clean
AT 0:36 and 0:48 are 2 examples of precisely what I'm trying to do.
I know my way around fusion, keyframes and masking etc, but I'm obviously lacking in the specifics of this particular endeavour.
Thanks in advance for any help.
I want to add a graphic to a video which is fixed/anchored to a certain point.
Specifically, I want to add a line or arrow that moves in relation to a moving object but stays anchored to a point in the clip which also moves.
https://torokhtiy.com/pages/clean
AT 0:36 and 0:48 are 2 examples of precisely what I'm trying to do.
I know my way around fusion, keyframes and masking etc, but I'm obviously lacking in the specifics of this particular endeavour.
Thanks in advance for any help.