Use the geocoding plugin to geocode feature data within a feature layer. This demo relies on the Esri Leaflet Geocoder plugin.
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Search for feature layer data (feature service)</title>
    <meta name="viewport" content="initial-scale=1, maximum-scale=1, user-scalable=no">
    <link rel="stylesheet" href="https://unpkg.com/leaflet@1.9.4/dist/leaflet.css" crossorigin="">
    <script src="https://unpkg.com/leaflet@1.9.4/dist/leaflet.js" crossorigin=""></script>
    <!-- Load Esri Leaflet from CDN -->
    <script src="https://unpkg.com/esri-leaflet@3.0.19/dist/esri-leaflet.js"></script>
    <!-- Load Esri Leaflet Geocoder from CDN -->
    <link rel="stylesheet" href="https://unpkg.com/esri-leaflet-geocoder@3.1.6/dist/esri-leaflet-geocoder.css" crossorigin="">
    <script src="https://unpkg.com/esri-leaflet-geocoder@3.1.6/dist/esri-leaflet-geocoder.js" crossorigin=""></script>
    <!-- Load Esri Leaflet Vector from CDN -->
    <script src="https://unpkg.com/esri-leaflet-vector@4.3.2/dist/esri-leaflet-vector.js" crossorigin=""></script>
    <style>
      html,
      body,
      #map {
        padding: 0;
        margin: 0;
        height: 100%;
        width: 100%;
        font-family: Arial, Helvetica, sans-serif;
        font-size: 14px;
        color: #323232;
      }
    </style>
  </head>
  <body>
    <div id="map"></div>
    <script>
      const accessToken = "YOUR_ACCESS_TOKEN";
      const map = L.map("map").setView([40.91, -96.63], 4);
      L.esri.Vector.vectorBasemapLayer("arcgis/navigation", {
        token: accessToken
      }).addTo(map);
      const arcgisOnlineProvider = L.esri.Geocoding.arcgisOnlineProvider({
        apikey: accessToken
      });
      const gisDayProvider = L.esri.Geocoding.featureLayerProvider({
        url:
          "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/GIS_DAY_Registration/FeatureServer/0",
        searchFields: ["event_name", "host_organization"],
        label: "GIS Day Events 2019",
        bufferRadius: 5000,
        formatSuggestion: function (feature) {
          return feature.properties.event_name + " - " + feature.properties.host_organization;
        }
      });
      L.esri.Geocoding.geosearch({
        providers: [arcgisOnlineProvider, gisDayProvider]
      }).addTo(map);
    </script>
  </body>
</html>