"DP charges are charged by the depository (CDSL). They are levied when the scrip is debited from the demat account. And it is calculated per scrip per trading day. So even if you sell the same scrip multiple times on the same day, you will be charged only once.
Eg. If you sell a share of TATA motors, you will be levied DP charges the first time but for all subsequent shares sold on that day, no DP charge will be applicalble.
The charge is Rs 13.5 + GST per scrip.