You specify the trigger conditions adding AO Trigger config.vi immediately before AO Start.vi, and selecting 'PFI Pin' for the Trigger or gate source terminal (create a constant from the terminal and select the correct option) and wiring the constant string 'PFI0' to the Trigger or gate source specification terminal.
Refer to the examples that ship with ni-daq, particularly 'Generate N updates using digital triggering' (Generate N Updates - E-series - D Trig.vi).
All this if your card does support this feature:I never used it so I can't help you in this matter, but you can find it referring to hardware capabilities in LabVIEW help.
Roberto