How about (remember that the item number is actually a string, not an integer):

1. Get all item numbers of a known value of 1:

var items = Job.Items.Where(x => x.Number == "1").ToList();

2. Get all item numbers of a known value of 1 and where the CID is equal to 2:

var items = Job.Items.Where(x => x.Number == "1" && x.CID == 2).ToList();

3. 

var items = Job.Items.Where(x => x.CID == 2).ToList();

            foreach (Item value in items)
            {
                 if (value.Number == "1")
                 {
                     // item number of 1
                 }
             //do stuff
            } 

Does that help at all?