A small hole appeared on the cat’s body with some fluid.

This wound is likely a purulent infection – from an unabsorbed injection or vaccine at the shot site, or from a fight, injury, or external-parasite bite. Shave the area and surrounding fur, flush the wound with hydrogen peroxide, disinfect the edge with iodine, and squeeze out the discharge or pus with gauze until slight fresh bleeding.

Apply external antibiotic ointment twice daily with oral anti-inflammatory and pain medicine such as pet anti-inflammatories and meloxicam for 10-15 days. An Elizabethan collar is mandatory, or it will not heal if licked.