You're not limited to your own organisation when it comes to requesting feedback. You can also request feedback from outside sources, such as clients, customers, business partners, etc...
If you want feedback from an outside source, just enter the person's email address in the search function. That person will then receive an email with your message and a request for feedback.
In the email the outside source needs to click on: Give [user's name] feedback!
Once the person answers, you will be notified by email and you will see the feedback on your feed!