Final answer:
The sales associate should refer to the product manual to find out how long it takes to charge the battery of the portable Bluetooth speaker.
Step-by-step explanation:
The sales associate should refer to the product manual to find out how long it takes to charge the battery of the portable Bluetooth speaker. The product manual typically provides detailed information about the device, including charging times and instructions. By consulting the manual, the sales associate can ensure accurate and reliable information, rather than relying on potentially incomplete or incorrect information from online sources, colleagues, or the instructor.