application.js

//= require jquery
//= require jquery-ui
//= require rails-ujs
//= require activestorage
//= require turbolinks
//= require_tree .

index.html.erb

<%= form_with url: admin_studies_edit_path, method: :get, local: true do |f| %>
<%= f.text_field :study_title, data: { autocomplete_source: admin_studies_path} %>         
<%= f.submit 'Search', class: 'button-special' %>        
<% end %>

studies.js

(function($) {
  return $('#study_title').autocomplete({
    source: $('#study_title').data('autocomplete-source')
  });
}(jQuery);

StudiesController.rb

def index
    @studies = Study.search(params[:term])
    respond_to do |format|
      format.html
      format.json { render json: @studies.map(&:title) }
    end
  end