* Uh-huh: This is the most common way to spell it out.
* Uhuh: A shortened version of "uh-huh".
* Hmm: This conveys a similar sentiment, but focuses on the "hmm" sound.
* Mm-hmm: This emphasizes the "hmm" sound, but also includes the "uh" sound.
You can also use emojis to express the sound:
* 🤔 Thinking face
* 🤨 Suspicious face
Ultimately, the best way to type "uh hmm" depends on the context and your personal preference.