General synonyms:
* Alertness
* Awareness
* Focus
* Heedfulness
* Mindfulness
* Observation
* Perception
* Vigilance
More specific synonyms:
* Thoughtful: Emphasizes consideration and understanding.
* Responsive: Emphasizes quick reaction and engagement.
* Engaged: Highlights active participation and interest.
* Intrigued: Suggests a feeling of curiosity and fascination.
* Devoted: Highlights a strong sense of commitment and care.
* Dedicated: Emphasizes a strong sense of purpose and focus.
The best synonym for "attentiveness" will depend on the context of your writing.