How can I Skew Numerically on a Smart Object layer??

One of the points of Smart Objects is that you can Transform them with complete freedom.  Type layers, for instance, can not be warped unless they are made into Smart Objects.  So you don't need to open the SO in a new window.

Here's and SO.  It has two layers and is off centre.

We need to drag a guide to its centre point, which means we need to start the Free Transform (FT) process, but not have it cancel when we move the cursor to far from the object, so we need to pan the canvas close to the ruler before we start FT.

I've done the above steps, and I have a guide that has Snapped to the centre handle (You might need to turn on the centre handle in Preferences.

I'll assume a horizontal skew, so we need a reference point.  I'll achieve that by dragging the ruler zero point onto the handle

I'm half a pixel out, but I hope you won't hold that against me.   Note I dragged in a second guide so you can skew whatever way you like

We only needed the guides so the zero point would snap to them, so we need to turn them off now.

Unfortunately, we still can't place the cursor in the X: field and type in an offset, but by hold down the Ctrl (Cmd) key we can see exactly how many pixels we have displaced the middle top handle, plus we have a heads up of the angle.  If you move the cursor to the X:field then it will move the entire object, and not continue to skew it.

That's the best workaround I can come up, but it does give you some numbers.

Smart object are encapsulated object. To modify them (like normal layer) you have to double click the layer thumbnail.