How many grams of carbohydrates should a person with type 2 diabetes or gestational diabetes intake a day?

No definite #: There is no definite # on that. It will depend on your prepregnancy weight, the weight you've gained throughout your pregnancy, the severity of your diabetes. The calorie intake increases in the second and third trimester by ~ 300 calories/day. Of which ~65% should come from carbohydrates.

Depends on exercise: The best approach is to eat 6 small equal meals a day with good quality protein, fresh vegetables, and colorful berries at each meal. The carbohydrates from fruit, a non starchy grain like quinoa, or non starchy beans like black beans or lentils with plenty of fiber in small meals will not elevate blood sugar especially if each meal is followed by about 10 minutes of walking or other moves.