Depends on what you’re trying to do - it’s fairly simple if you want to update a field (on a newish version of Skuid) or run a branch action. Both can take formulas for doing a calculation, so you just need to do a modellookup that finds the last row of the model. It’s something like…

Add a ui-only formula field (uiIndex) on the object, number, and have the formula be {{index}} (returns the row .

In the update as result of formula, do something like MODEL_LOOKUP(“model”,“FieldYouWant”,“uiIndex”,{{$Model.model.data.length}} - 1)