Most doctors recommend a blood sugar of below 100 when fasting, and not over 140 two hours after eating. Most of the time, a non-diabetic person will never hit the 140 mark, but for a Type 2 diabetic, this is how he or she can tell if a particular food will spike the blood sugar.
Really, the only reliable way for a T2 diabetic to keep an eye on his or her condition is through frequent blood sugar tests. Some diabetics test four or five times per day, and this helps them monitor what works for them and what does not.
Most diabetics will get an idea of when their sugar runs higher and lower and can log it in a booklet so they can show their physician their averages during the day. This helps the doctor adjust medications and so forth.