That depends on your current hiking skills and which sites you wish to explore during your Petra visit. For instance, if you head to The High Place of Sacrifice, expect a relatively steep climb; on the other hand, there’s Petra’s Main Trail, which is a flat, easy path.
Upon your arrival in Petra, you’ll receive a map outlining key sites and trails, together with walking distances and difficulty levels, so this should help you decide which trails to check out and which ones to avoid.