You didn't clearly understand what he was saying.
Or
You clearly didn't understand what he was saying
The second one is better. Don't separate the auxiliary verb and the main verb. You clearly didn't understand what he was saying.
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The second one is better. Don't separate the auxiliary verb and the main verb.
You clearly didn't understand what he was saying.
Iron ManYou didn't clearly understand what he was saying.
~ did not understand in a clear way (whatever that may mean)
Iron ManYou clearly didn't understand what he was saying
~ It is clear (to all) that you did not understand ...
CJ