You may talk to Jakaka at (I-10) to learn more about where Rockhoppers may be located. This is not required to continue with the quest.
Head to (I-10) near the south wall. You will find a patch of grass and bones with many Ignis Eruca around the area. They detect by sound during the day so make sure you have a form of sneak up while performing this. Stand inside the triangle formed by bones in the corner.
Perform a /clap emote and quickly tab around. If you find a Rockhopper target, click it quickly. If you take too long, it will disappear. The Rockhopper moves around small amounts, so it's best to just stand in one spot and clap until it works. You will see a small sparkle on the ground when it appears.
I suggest NOT tabbing around, but rather to set the camera to as much of bird's eye view as possible, and to look for the sparkle of the Rockhopper on the ground.
You must be fairly close to the spot to get the Rockhopper, else you will get a "Target out of range." message. Walking around while clapping is a viable strategy, but you must spot and use the Rockhopper target quickly.
"/clap motion" does work to draw out the Rockhopper. As this is a fairly popular experience spot, consider macroing this instead of just using /clap.
typing /clap and using the up key is of course more than fast enough. Clap fast, no time to lose.
Find a Gasponia and check it (near Veridical Conflux #04). If you receive the message "This gasponia is exuding a pleasantly mild scent", you must find another gasponia to inject as the current one you are at has been recently injected. The correct message is "You inject the phial of counteragent into stalk of the gasponia.".