Eiablagen Tagfalter

Kevin pretty much summarized that perfectly. Butterflies do only lay on the food plant, with some exceptions like some Satyrinae which just drop their eggs to the floor. But other than that, the question is far too generalized to give any meaningful answer. Every species is different and needs special conditions. Some are extremely hard to get to lay eggs in captivity. Generally, it is much harder than with most moths. Usually the three main things are: Keep them well fed, leave them room to fly around but assure that they make contact with the host plant every know and then, and lastly they need sun and warmth. Unlike moths, most butterflies are inactive when the temperature is lower than around 20-25 °C. The activity of some species also heavily depends on sunlight. If there is no light that provides heat (infrared) they won't get active and therefore won't lay any eggs.

Greetings Dennis