How to output Pref aov in maya arnold

[wsc12321]

I add Pref aov in render setting tab in maya to output Pref pass.But,there's nothing when rendering.It's all black.does anybody know how to output Pref pass in maya arnold correctly with details?thanks a lot.

[Stephen.Blair]

Put a texture reference object on something?

[wsc12321]

excuse me,what you say means assign a shader on the object or create some attributes to the object?could you show me some details？thx

[wsc12321]

ok，I‘ve known how to do that,thx a lot

[wsc12321]

I have some new problems.do you know how to output Pref of fur(Yeti)