The diesel engine oil filler cap is located on top of the engine; adding diesel engine oil here is the correct method. The hydraulic transmission fluid filler cap is located on top of the transmission; this is the correct location for adding hydraulic transmission fluid.
To add brake fluid, locate the master cylinder; the brake fluid reservoir is usually located above the clutch (micro-clutch) pedal. Please note that when adding engine oil, always refer to the specific forklift model and owner's manual to ensure correct and safe operation.