Solution
Current will always flow from the positive connection to the more negative connection. When using the PXIe-4322, the positive lead of the load should connect to the AO+ terminal, and the ground lead of the load should connect to the AO- terminal, as shown below:

The PXIe-4322 has a nominal current range of +/- 20 mA. Therefore:
- If the current output is set to a positive value, current will flow from AO+ to AO-.
- If the current output is set to a negative value, the flow of current will be reversed (i.e. from AO- to AO+).