What is superlative of fluently?

There is no superlative form of "fluently". "Fluently" is already an adverb describing a high degree of fluency, and it's not something you can make "more" or "most" of.

Here are some options you could consider instead:

* More fluently: If you need to express a higher degree of fluency than "fluently" alone.

* With the utmost fluency: A more formal way of expressing the highest level of fluency.

* Effortlessly: This can suggest a level of fluency that appears effortless, implying a very high level of skill.

* With remarkable ease: Similar to "effortlessly" but emphasizes the ease with which the skill is performed.

The best choice depends on the specific context of your sentence.