Hi Martin,

You'll need to inject an IScopeProvider into the constructor of your class, along with an IUmbracoFactory. This is achieved using Dependency Injection. The docs are pretty good at explaining what's going on, read here.

I've taken the liberty of refactoring your code a little to get it working:

using System.Linq;
using Umbraco.Core;
using Umbraco.Core.Composing;
using Umbraco.Core.Events;
using Umbraco.Core.Scoping;
using Umbraco.Core.Services;
using Umbraco.Core.Services.Implement;
using Umbraco.Web;

namespace OnDocEvents.Components
{
    [RuntimeLevel(MinLevel = RuntimeLevel.Run)]
    public class MyComposer : IUserComposer
    {
       public void Compose(Composition composition)
        {
        composition.Components().Append<DocEvents>();
        }
    }

    public class DocEvents : IComponent
    {
        private readonly IUmbracoContextFactory _umbracoContext;
        private readonly IScopeProvider _scopeProvider;

        public DocEvents(IUmbracoContextFactory umbracoContext, IScopeProvider scopeProvider)
        {
            _umbracoContext = umbracoContext;
            _scopeProvider = scopeProvider;
        }

        public void Initialize()
        {
            ContentService.Published += ContentService_Published;
        }

        public void Terminate()
        {
            ContentService.Published -= ContentService_Published;
        }

        private void ContentService_Published(IContentService sender, ContentPublishedEventArgs e)
        {
            var node = e.PublishedEntities.FirstOrDefault();

            if(node == null)
            {
                return;
            }

            using (_scopeProvider.CreateScope(autoComplete: true))
            {
                using (var contextReference = _umbracoContext.EnsureUmbracoContext())
                {
                    var context = contextReference.UmbracoContext;
                    var content = context.Content.GetById(node.Id);

                    var url = content.Url;
                }
            }
        }
     }
}