It's not a rash. I think Shukla injured his hand during last week's luxury budget task. The cut looks kinda like alphabet R so Bhau was teasing him ki Rashami ko bolta hai haan kardo kyunki Shukla ne uske liye haath kaat liya.
Btw, When they were teasing Shukla, he said that "woh" karti hai yeh sab and uske haath pe nishaan bhi hai. Is it true? I have never seen any cut marks on Rashami's hands. What was he talking about?