Matthew 13:51
"Have you understood all these things?" [Jesus asked]. "Yes," they said to Him.
Matthew 15:16-17
And He replied, "Are you still unable to understand?
Matthew 16:11
How is it that you do not understand that I was not speaking to you about [physical] bread? But [rather I meant] watch out for the yeast [i.e., the influence] of the Pharisees and Sadducees."
Mark 4:13
And Jesus continued to speak to them, "Do you not know what this parable means? Then how can you understand any of the other parables?
Luke 9:45
But they did not understand what He was talking about, for it was hidden from them, so that they would not understand its meaning. And they were afraid to ask Him about what He had said.
Acts 8:30
So, Philip ran over to it and [when he got near enough] he heard the Ethiopian eunuch reading from Isaiah the prophet and asked him, "Do you understand what you are reading?"