My daughter had a dark spot on x-ray on leg, below the knee. dr. said she'll have the radiologist look at it. what could it be?

Several things: Wait for the radiologist's opinion. This is a problem that necessitates a face-to-face meeting with your doctor. This will allow him/her to examine you, ask specific questions. And possibly order tests to find out what's wrong and what to do to help you.

Benign or malignant: A tumor at the knee in a child is usually benign. However, there is a high frequency of malignant masses at the knee in kids.