I did a quick search here at GF & came up with this...
"Malnutrition, dehydration and physical trauma can cause a gecko's tail to look like that (refers to another picture, not yours). Correct any potential causes of the first two and do what you can to prevent further trauma and hopefully the condition will not worsen."
If your friend has any questions about how to take care of the gecko, send her/him here & the questions will be answered.