Why it say's mypallete is undefined?

I have declared my own paltte in planogram.html as shown below
myPaletteAssembled.model = new go.GraphLinksModel([
{ key: “Rackassembledpatchpanel”, color: green, source:“cat6assembledtotalrack.png” ,size: “100 100”},
{ key: “Rackassembledpatchpanel”, color: blue, source:“cat6assembledtotalrack.png” ,size: “100 100”},
{ key: “Rackassembledpatchpanel”, color: yellow, source:“cat6assembledtotalrack.png”,size: “100 100” }
]);

myPaletteAssembled =
      $(go.Palette, "myPaletteAssembled",
        { // share the templates with the main Diagram
          nodeTemplate: myDiagram.nodeTemplate,
          groupTemplate: myDiagram.groupTemplate,
          layout: $(go.GridLayout)
    });

When I run the Example planogram.html I get the error "Uncaught reference error “myPaletteAssembled” is not defined

Are you trying to assign the model before initializing the palette?

Yes thanks that was the problem but in this Example when I sense that some palatte has been dropped I need that to be replaced with my myPaletteAssembled and I tried using myDiagram.model.addNodeData(myDiagram.findNodeForKey(“Rackassembledpatchpanel”)); but I do not see that node
on the background . Do I need to make something visible or I need to use some other call ?

What do you mean by “some palette has been dropped”? Is the user supposed to be dragged HTML DIV elements around, each representing a diagram?

Remember that the data objects in a model are just plain JavaScript objects – they are NOT instances of the Node or Link class! Nodes and Links belong to Diagrams; data belong to Models.
https://gojs.net/latest/intro/dataBinding.html#RelationshipsOfPartsAndDataAndBinding

myDiagram.model.addNodeData(myDiagram.findNodeForKey(“Rackassembledpatchpanel”));
This does nit show my palette on the background

Please heed what I just said.

Also, please use go-debug.js and pay attention to any warning or error messages in the console window.