In all honesty, it is kind of tricky to find the feedback.
One way to do it is to go to your list of past contracts and look at the contracts individually.
An easier way is to look at one of your current or past job postings, and look at the page that shows the job posting as freelancers would see the job posting.
This should show your "job history" (jobs you hired for in the past) along with freelancer feedback.
But the tricky thing is that THERE IS NO "client profile" page where you can easily go and look at the job history at the bottom of the page, and see all the feedback, similar to what you can see for freelancers.
For most of the new freelancers it's a bit difficult for them to find out but it's really easy. Below main header for that contract you will see give feedback there you can easily leave feedback for your client.
Also you may check out the feedback from contracts