You have a small network of devices connected together using a switch. you want to capture the traffic that is sent from host a to host b. on host c, you install a packet sniffer that captures network traffic. after running the packet sniffer, you cannot find any captured packets between host a and host b. what should you do?

OK. Sounds like you are trying a MiTM (Man-in-The-Middle) attack. Depends on what packet sniffer you used.
If you are interested in penetration testing i recommend installing Kali Linux. If you are working with a WiFi network you will need an WiFi Adapter that supports monitoring mode.
Here is a list:
https://null-byte.wonderhowto.com/how-to/buy-best-wireless-network-adapter-for-wi-fi-hacking-2017-0178550/

Hope this helps. ;)