Look at the person's profile, and take note of his/her user number from the address bar. Then look at someone's feedback (where his/her feedback number is visible from his/her post. Then just substitute the user number in the address bar with the earlier number you noted.
Let me add the next steps to paolorenzo's suggested procedure:
Proceed to the newly created web address (URL). This will take you directly to the
SMF Trader System-Trader Overview page of the member/recipient of the feedback. Click
Submit feedback for (handle name) on the lower left part of the page.
While dpog's procedure is the most direct way of leaving a feedback, it only works if the member has an existing post in the forum.