Short answer: some Jains eat groundnuts, and some do not. It depends on local practice and the specific Jain tradition you follow.

Why some Jains eat them:

• Jain diet is guided by ahimsa (non-violence). Groundnuts are plant-based and can be part of a lacto-vegetarian diet for many Jains.
• For many people, eating legumes like groundnuts is a convenient way to get protein without harming animals.

Why some avoid them:

• Some Jain communities avoid seeds/beans or underground legumes because of concerns about the life in seeds or the extra harm that can come from harvesting underground pods.
• A few strict followers avoid all seeds or certain legumes as part of their further effort to minimize harm to living beings during cultivation and harvest.

Because there are differences between Digambar and Shwetambar traditions (and even regional practices), the most reliable answer for you is to ask your local Jain teacher or community leader. They can tell you what is preferred in your tradition.

If you’d like, tell me your tradition (Digambar or Shwetambar) and your region, and I can share the standard practice for groundnuts in that context.