General synonyms:
* Thinking
* Understanding
* Perception
* Knowledge
* Awareness
* Mental processes
* Reasoning
* Intelligence
More specific synonyms:
* Memory: If referring specifically to the process of remembering.
* Attention: If referring to the ability to focus on specific stimuli.
* Learning: If referring to the acquisition of new knowledge or skills.
* Problem-solving: If referring to the ability to find solutions to challenges.
* Decision-making: If referring to the process of choosing between options.
The best synonym for "cognition" will depend on the specific context of your writing.