The answer to the first part is simple, ask about anything you do not yet know or understand and keep asking until you do understand. The answer to the second part is much more complex.

You should always be aware of what you say and how you speak when in the presence of a patient. This awareness includes times when you might be out of sight but not completely out of earshot. Ask any questions that pertain to something out of the ordinary being discovered on the image after leaving the bedside. Questions about scanning techniques can be very appropriate during the scan but be sure to inform the patient in advance that you are a student and may be discussing some of these things with the experienced sonographer. Even when discussing scanning and normal anatomy in front of a patient, it is important to be careful of phrasing. Always be mindful of how something you say may be interpreted or misinterpreted. Remember, the patient and any loved ones in the room are very likely anxious and even an innocent question such as “What is that?” may be translated in their mind into “Something is terribly wrong in there.”

This is where a notebook and pen will come in very handy, especially during the observation phase of learning. Write down questions when you think of them, that way you will be sure to get them answered after. It can also be helpful to tell the patient that you will be taking notes. After moving into a phase where you are scanning with a teaching sonographer, it is useful to develop a wordless communication with the sonographer who is observing you. Doing things such as placing an arrow on anatomy you are unsure about but want to discuss later will help both of you to remember, even if you do not take the image with the arrow in place. Simply moving the arrow around in a circle in an area of the image can be enough to tell the sonographer that you want to talk about this later. She can also signal you by the same method.
When you finally move into a phase where you are scanning alone for a time then having a sonographer come in after you, take the time to discuss any questions before you both re-enter the room. That way she or he will specifically know where to concentrate. Communication between you and a supervising sonographer is probably the most important aspect of learning. Do not let something you do not fully understand slip by undiscussed.