How to infer the max current output of this function generator from its datasheet/specs?
This function generator has a 50\$\Omega\$ output impedance and is protected from short circuits. To me, this implies that the maximum current is limited by the open circuit voltage (up to 20V) and the output impedance. Ohm's Law says the maximum output current should be 400mA when the output is shorted or 200mA into an external 50\$\Omega\$ load.

Having said that, it makes me uncomfortable that there is no specification for the output voltage range with a 50\$\Omega\$ load. It may be that the sheet you linked is an abbreviated version of the full specifications.