Need your help on the following topic. I have a list of columns, and I wd like to take each column in turn (column n) and combine this column contents with the contents of column i which is NOT fixed.
Is there any Loop Node that could solve this?
Yes, you can use the Column list Loop start, the column combiner and the Loop end (column append) nodes. Just make sure that you exclude the node that you always want to use for the concatenated string in the first node.
If the second column also is not fixed as you say you could go with a "Table Row to Variable Loop" and use a table where each row contains the columns to be combined for each single iteration. You can use flow variables to pass the relevant columns to the "Column Combiner" node. If the second column is indeed fixed (i.e. always the same column) then agaunt's approach is the way to go.