The example of sentencing someone from the options provided is: "The judge tells a convicted defendant that she must pay a fine." This is because sentencing refers to the process of imposing a punishment or penalty on someone who has been found guilty of a crime. In this case, the convicted defendant is being ordered to pay a fine as part of their sentence.
The other examples listed are not examples of sentencing. The judge telling a witness to repeat what they said is an instruction, the judge telling a defendant to take an oath to tell the truth is an order related to courtroom procedure, and the judge telling an attorney that they cannot ask a particular question is a ruling related to the admissibility of evidence.