Hi,
I haven't used Wwise in Unity. But a sequencer command is the way to go. You can find a starter template script in Plugins / Pixel Crushers / Dialogue System / Templates / Scripts / SequencerCommandTemplate.cs. Just copy it and fill in your code where the comments indicate. It will then show up in the Sequence field's "+" dropdown menu and/or you can type it manually into the Sequence field.
The manual has a section with
Cutscene Sequence Tutorials. Part 6 covers custom sequencer commands. You can also refer to the
Cutscene Sequences section of the manual.
If you want to see how the built-in AudioWait() sequencer command works, you can examine the source (SequencerCommandAudioWait.cs). For your Wwise command, you probably don't need to implement everything that the AudioWait() command does. It's designed to be able to handle a lot of different cases.
To see the AudioWait() command in action, play DemoScene1 and talk to the NPC. The Dialogue Manager's Default Sequence uses AudioWait().