Like you would any wire?
Most wire people put ink marks on the wire or small tape flags and then measure elongation with optical trackers.
I have done this with wire that only had 0.5% elongation at fracture.
if using optical trackers, can it track the mark on the wire if the wire move to other position? in my case, the wire is subjected to shear loading (eg: as attached).
Not the old units, but I presume that the technology has improved significantly.
You might need to talk to optical guys that are not in the testing business, but I am sure that it can be done.