EMAGENT_HOME is set in the environment. Ideally this should be in the .profile for the 'oracle' user. For example:

export EMAGENT_HOME=/u01/app/em12c/agent_13.1.0.0.0 # Database Servers

EMAGENT_HOME is likely to be different on the OMS. Ideally this should be in the .profile for the 'oms' user. For example:

export EMAGENT_HOME=/u01/app/agent12c/agent_13.1.0.0.0/bin # OMS

cd $EMAGENT_HOME/bin

./emctl status agent

To determine which agent is running (and from which location)...

ps -ef | grep oracle | grep agent

The result of the command below should be the URL of the agent. Try it in a browser to prove agent connectivity....

cd $EMAGENT_HOME/bin

./emctl status agent | grep "Agent URL" | grep -v "Local" | awk -F" : " '{ print $2 }'