This generally happens in two ways. First is when the Mormon lay leader of a congregation (usually the bishop and always a male) calls in the boys and girls in his flock from age 12 on up for an annual interview to ask about their testimonies, church attendance, faithfulness to the LDS health code (called the Word of Wisdom) and adherence to the law of chastity.
Some bishops pose pointed questions about moral cleanliness in these conversations, perhaps quizzing about masturbation, heavy petting or fornication, while others keep their queries more general.
The other type of interview is when penitent members go to their bishops to confess actions the church deems to be “serious sins.