I find that a simple way to assess for listening skillfulness is asking people whether they think they're good listeners. The more eager or adamant the yes, the more curiosity needs to be applied. For any response, it's interesting to ask how they know.
This inquiry gets particularly interesting when we talk about listening as unfolding and discovering the unspoken context for the content shared. That someone says they hear the content of everything said in no way guarantees they are also aware of the context of everything unsaid. Good listening is contextualized listening. Good listening is complete listening.