包丁 should be a larger knife which is used for cutting vegetables or meats. So, it is used to prepare large meals. (espeiallyespecially suitable for eastern asianAsian cuisine)
ナイフ should be a smaller knife which is used for cutting fruits or cakes. So, it is used to prepare desertsdesserts or something not so large meal. (especially suitable for western cuisine)
In addition to food preparation, ナイフ is used to describe a table knife (e.g. for eating a stakesteak) or an army knife (e.g. to protect yourself). We do not use 包丁 in thethese situations.