Those brakes look similar to old DAP brakes I had. There is no fluid resevoir on the master cylinder. To bleed them your best bet is some form of pressure bleeder. You can improvise a cheap pressure bleeder from a squeeze bottle with a tapered spout (like a catsup bottle) or purchase something more expensive. Start by removing a bleeder screw (one of the allen screws next to the brake line) at the caliper, then remove the filler plug (above the brake line) on the master cylinder. Twist the tapered end of the pressure bleeder bottle into the filler hole of the master cylinder and squeeze. Let the fluid run out of the caliper bleed hole until you stop getting bubbles, then re-install the bleeder plug while maintaining some pressure on the bottle to keep air from getting back into the caliper. (This may take 2 people.) Remove the bottle from the master cylinder and top off the master cylinder with brake fluid before re-installing the filler plug. It's OK for brake fluid to seep out as you install the filler plug, but clean it off afterward. (Brake fluid can damage paint.)
I would advise checking with someone familiar with that brand of brakes before buying fluid. Most kart brakes use kart (silicone) brake fluid, but the DAP I mentioned used automotive brake fluid. Using the wrong fluid can ruin the seals in the master cylinder and caliper!
Just from looking at the picture of the master cylinder I'd also suggest backing off the adjuster nuts on the linkage. It may not be retracting all the way. You can reset and tighten them as necessary after bleeding.