Here are some options depending on the context:
For "reflect" as in "to think deeply":
* Pensive
* Contemplative
* Introspective
* Meditative
* Thoughtful
* Reflective (this is a common adjective form of "reflect")
For "reflect" as in "to show an image":
* Mirrored
* Shiny
* Glossy
* Polished
* Reflective (can also be used in this context)
For "reflect" as in "to demonstrate something":
* Illustrative
* Indicative
* Representative
* Symbolic
* Expressive
To choose the best adjective, consider the specific meaning of "reflect" in your sentence.