The celebrated mummy is kept at the tiny settlement of Sumpaima, 300m north of Jiwika along the main road from the main village entrance (look for the black ‘Mummy’ sign). Wimontok Mabel was a powerful 18th-century chief here and his blackened corpse is the best preserved and most accessible of its kind near Wamena.
You will likely be asked for around 130,000Rp per person for a viewing. You can try bargaining but don't expect much of a reduction.