An example of a page where you can find many torrents search engine is https://github.com/qbittorrent/qBittorrent/wiki/Unofficial-search-plugins
Go into this page and choose one for example LimeTorrents and press download:
Copy the URL and Back to eMule and press Web Link. Paste the Link and press ok, the new search engine will be already added to eMule.
If you have on your computer the search engine file, you just must press local file, look for the file and press Open. The new search engine will be already added to you eMule.
This is way you can add torrent search engines to eMuletorrent.
eMule is available for Mac and Windows on www.emule.com