To get a job and eager load all its quotes and their quoteitems, you write:
var job = db.Jobs
.Include(x => x.Quotes.Select(q => q.QuoteItems))
.Where(x => x.JobID == id)
.SingleOrDefault();
You might need SelectMany instead of Select if QuoteItems is a collection too.
Note to others; The strongly typed Include() method is an extension method so you need to include using System.Data.Entity; at the top of your file.