Negi surely got his scar (on the left cheek) during the Mahora Tournament.
It isn't quite clear whom it was among Takamichi Takahata or Setsuna Sakurazaki caused the scar. Whether it was because of Takamichi's kanka punch grazing his cheek, on ch 98 pg 5, or because of Setsuna's claw attack, on ch 115 pg 18. Both attacks were on the same cheek, and both have enough proximity to the scar left.
However, I believe that this scar was cause by Setsuna as it was mentioned on ch 225 pg 11.
See the related links for the pages that his scar is mentioned on.
The most notable ones are the scar on his left cheek, and the one on his right arm. The first scar, the one on the cheek seems to have become permanent (although at times, the scar isn't visible in the drawings with negi's face facing forwards; such as in volume cover 21 or 22?) The second is the scar caused by the "Nagi" illusion created by Albireo Imma (Colonel-san)'s artifact and hence, Negi has allowed the scar to be left untreated since he considers it as a memento of his father. There is also the scar from having his right arm sliced off by Kagetarou, but it isn't clear yet if it will be permanent since it hasn't been that long. I think he can use some kind of magic or magical item (like the lotion he used on ch 255) to erase those scars, but he decided to keep the scars as a reminder of those events (it mentioned on ch 255 pg 11 and ch 120 pg 4). Here are the links: Ch 255 pg 11 (When he explain why he left his left cheek's scar) http://www.onemanga.com/Mahou_Sensei_Negima%21/255/11/ Ch 120 pg 4 (When he explain why he left his right arm's scar) http://www.onemanga.com/Mahou_Sensei_Negima%21/120/04/
Probably a prison scar
she got cut
The man had a scar on his cheek. A scar may or may not be noticeable.
Olivia Wilde - "I've got a scar on my right cheek, I scratched myself when I was only some hours old".
hot playdough when she was a kid
No. A British soldier did.
Al Capone was known for his distinctive facial feature, a prominent scar on his left cheek, known as a "knife slash" or "knife wound." The scar was a result of a fight in his younger days, earning him the nickname of "Scarface."
Danica Patrick acquired the scar on her right cheek from a childhood accident. When she was around nine years old, she fell and cut her face on a rock while playing outside, leading to a scar that has become a recognizable part of her appearance. Despite the injury, Patrick has often embraced her scar, viewing it as a part of her unique identity.
Tina Fey
he got shot once with a gun pointed inside his mouth, but he was lucky, the bullet only pierced though his cheek
Montag has a permanent scar on his cheek from a burn caused by his father.