Beef Jerky is good for weight gain if you eat enough of it.
I used to eat a lot of beef jerky as a snack and because I craved it and when I ate too much beef jerky I gained at least 20 lbs of weight in a year of eating a lot of beef jerky.
Although beef jerky is not very healthy and should only be eaten in moderation the beef jerky is a pretty good snack and you should gain some weight eating it.
However you can gain more weight faster by eating other meats and other higher calorie foods.
You can also gain weight by taking weight gain supplements which helps you increase your weight.
Just don't gain too much weight too fast as that can be unhealthy and as long as you're a healthy weight I would not recommend increasing your weight.
Because the more you weigh the more your heart has to work and weighing too much can increase your chance of dying too early and cause heart attacks.