Re: DOMO Dataset : Adding new column to the existing schema.
To add a column to an existing dataset, you would either need to add the column at the source of where it is coming from (i.e. via Workbench and SQL query) or create a dataflow with Magic ETL and add the new column there.
If you haven't created a Magic ETL before, I suggest reading this KB article. https://knowledge.domo.com/Prepare/Magic_Transforms/ETL_DataFlows
Domo makes it very easy to drag and drop various functions into your ETL and perform different actions. Once you have added your new column, add an ouput dataset and give it a name and then you will have a dataset with your new column.