Which enchant on Skarner?

Gargoyle in the vast majority of cases: Skarner engages and takes aggro, Gargoyle's massive shield lets him stay alive while allies follow up. Glorious only if the team lacks mobility to follow his engages.

When to take Mercury's Treads over Plated Steelcaps?

When the enemy composition has lots of CC or magic damage. If a champion like Morgana can cancel his engages with Black Shield, Mercury's also reduces the impact of return CC.

Can Skarner play without Zeke's Convergence?

Technically yes, but Zeke's turns each Impale into a team-wide slow amplification. It is one of the rare items that multiplies the value of Skarner's ultimate for the entire team. Replacing it must be justified by a very urgent defensive need.

Skarner Wild Rift Best Build Guide (Patch 7.2a)

The three core items serve three distinct functions: Searing Crown ensures passive pressure without depending on allied burst, Zeke's Convergence turns each Impale into a team-wide amplification window, and Thornmail counters AD carries that would otherwise be hard to keep locked down. These three…