I want to gain some weight.for that purpose,should i prefer nutella or peanut butter?and like in how much quantity

Be careful: With either. If you are trying to gain weight, don't just focus on the addition of one food stuff. Nonetheless, in the case of the two food stuffs, peanut butter tends to have less sugar and vegetable oil than Nutella(55% sugar!), so you should probably focus more on peanut butter. How much is difficult to say, as it depends on many things like your age, weight, activity level, etc.

Peanut butter: Without knowing your current weight and your baseline caloric balance, I can't give you a specific quantity. The number of calories/serving is on the nutritional label Consuming over time about 3000 more calories than you burn off produces ~ 1 # wt. gain. Peanut butter is better choice because fewer calories are from refined sugar. Weight training will encourage lean muscle wt. gain over fat.

Neither: Nutella contains 70% saturated fat and processed sugar by weight and peanut butter contains 50 grams of fat in a 3.5 ounce serving. Not the healthiest foods for your body. Peanut butter is susceptible to a mold that produces Aflatoxin, a known carcinogen. Advice for gaining weight is hard to give without knowing more about your goals and your current BMI.