Walking. After inguinal hernia surgery, strenuous exercise is contraindicated for a period of time, depending on the type and complexity of repair. A period of rest (1-2 days) followed by walking as tolerated is best. You cannot strengthen the tissues with exercise before or after this type of surgery but you can cause failure or chronic problems by over stressing the repair.
Abdomen and legs. The core muscles include hip flexors, abdominal wall, and back. A physical or occupational therapist can get you in a program that is best for your situation. The presence of a hernia shouldn't stop you from exercising, but may cause you to limit activity based on discomfort. This is true after hernia repair as well.
Plank. Core strength is best approached in a "multidisciplinary" way. By that i mean using many different exercises are best. Holding plank position, upper ab crunches, lower an crunches, hanging crunches. Many options. If you are under 50 with no heart diesase and in fairly good shape i recommend to my patients the p90x series, or insanity series. After appropriate recovery from surgery of course.