What is another word for listen as an adverb?

There isn't a single perfect word that works as an adverb equivalent to "listen." However, depending on the context, you can use phrases like:

To emphasize paying attention:

* Attentively

* Carefully

* Intently

* Closely

* Eagerly

* Thoughtfully

To emphasize obedience:

* Obediently

To emphasize understanding:

* Comprehendingly

To emphasize willingness to hear:

* Openly

To emphasize passively:

* Passively

The best choice depends on the specific meaning you want to convey.