How do I check if a device has universal forwarder installed and if so how do I troubleshoot while it's not sending data to the indexer.
To see if a UF is installed, look for the /opt/splunkforwarder directory (\Program Files\SplunkUniversalForwarder on Windows) or the /opt/splunkforwarder/bin/splunk file (\Program Files\SplunkUniversalForwarder\bin\splunk.exe on Windows). Be aware that admins can specify alternative installation locations so these paths could be different.
See https://community.splunk.com/t5/Getting-Data-In/What-are-the-basic-troubleshooting-steps-in-case-of-... for good troubleshooting tips.