It is an UI question. I can use the xyz-coordinate node to select a point by entering numbers for inserting a family on the Revit xy-plane. Does Dynamo have a node I can pick a point manually on a Revit plan view?
That depends on the logic of you floor plan.
If my building grids were placed on a certain coordinate with a certain plan to it, it could be easy, even when it was rotated.
So what i mean to say is, do you have any sense of where your building is located relative to one of Revit’s built in coordinates systems? You would not need a new point in the model.
But if you don’t have that, you can always find the intersection of say grid a and grid 1 and go from there.
My intention is picking a point on the Revit plan view (ground level), then Dynamo will insert a generic family (a simple 2d line family on the xz-plane) to the point the user pick. It is more about the usability. It is a little easier than measuring and entering the xyz coordinate numbers. It is similar picking an element in Revit environment from Dynamo. I don’t know if it is possible simply picking a point.
I found Clockwork “Element.Location” can kind of do what I want to do. It is not ideal that I need to place a benchmark family on the xy-plane first.
Try 
Its in the Sastrugi package
Use the Point.X Point.Y and Point.Z nodes
Those lists are a very good tool when you need to place a lot of components in Revit
https://primer.dynamobim.org/04_The-Building-Blocks-of-Programs/4-1_data.html
<1> means take the first level of lists
<2> would mean take the items in a list of lists (nested list)
All this can be found in the Dynamo Primer and the Designscript language.
DesignScriptGuide.pdf (3.7 MB) DesignScriptDocumentation.pdf (705.5 KB)