Good communication skills doesn't mean that you should have fluent in speaking. It is what you understand and let understand others with your opinion.
You should grasp understanding the task requirement.
If you are in hiring how do you test for the same in a candidate?
If the candidate is able to understand what you ask and able to answer in his/her way, then you may know how proficient in communication.
Sometimes, I feel difficult understanding the requirement for the task. I ask repeatedly. Asking questions repeatedly is not a bad practice but it will be bad when you don't understand the same thing. It is a sign of poor communication. Poor communication can happen from both side. It doesn't mean that if candidate doesn't understand what you say due to his/her capability. It might be your own fault making people understand what you say about.
Thus, things to consider while having communication:
In my personal experience, I have faced such problem. So, I would like to suggest:
If candidate forgets the talks, that will also state a poor signal of communication. So, better to graph in mind and in written.