Odd to even imagine a monk using a shield. I guess if he had to tank and was focused on survival more than dps, he might. But then monks are rarely used as tanks.
If you're not interested in "speculation", you're unlikely to get non-speculative answers here. To avoid speculation, someone needs to equip an "all things being equal" pair of monk and sk with a shield and the same weapon and parse a lot of fights. Generally, also an ideal monk primary is going to be different from a sk's ideal primary so you'd be adding variables that aren't realistic.
Why the question? If we knew the ultimate goal of this question, that might help. I'm more curious why the question than I am the answer, but that's just me.
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