Technically, the Analog Outputs of USB-6009 are only Voltage, you can compute the voltage required to result in a current into a "known" load.
But, the outputs cannot source more than 5mA typically.
For example, if you have a 1k resistor connected to AO and GND, now, to force 1mA into the resistor you need to configure the DAQ to output 1V, if you need 10mA, you need to configure to source 10V but limited by hardware it will be limited to just 5mA.
What are you trying to achieve? you can buy a proper hardware to source current or build an external circuit that can translate this voltage into current.
If you're trying to control 4-20mA loop, search ebay or Amazon for simple board that convert 0-5V to 4-20mA.