He died on 2 April 2005 and was first buried in the Vatican Grottoes beneath the basilica. In the days after his beatification on 1 May 2011 the coffin was moved upstairs to the Chapel of St. Sebastian, where it remains. The slab then read "Beatus Ioannes Paulus PP. II"; he has been a saint since 27 April 2014.
Because the chapel sits beside the basilica's main visitor flow, the area in front of it can be crowded, and at times it is closed off or kept for prayer. Access to the basilica itself, security screening and any reservation system change from time to time, so check the basilica's current arrangements before you go. Give the tomb its own few minutes instead of passing it on the way to the Pietà.
Bold Pilgrim's Rome & Assisi outline includes a visit to St. Peter's with time for prayer; a pilgrim who wants to pray at this tomb should say so when planning.