The task that was most likely the most difficult aspect of constructing an obelisk is erecting the obelisk.
Obelisks are massive stone structures, often weighing several tons and measuring many meters in height. The challenge of lifting them upright and securing them in place would have required advanced engineering techniques and considerable manpower, making it a significant obstacle compared to the other tasks listed. Engraving, coating, and painting, while also complex, could be accomplished after the obelisk was erected and would not involve the same level of logistical difficulty.