Hi,
and welcome to the KNIME Community.
To denormalize the prediction the name of the column with the predictions has to be the same as the column name of the target value in the normalizer node. We can therefore define a customized name for the prediction column in the configuration window to the "Predictor node".
But we have to have in mind that the column names are unique and KNIME will add a (#1) if we have already a column with this name. This means that in case of a test set where the target variable is available we would have to use the denormalizer node twice.
Did this help already? Otherwise I can provide you also an example.
Cheers
Kathrin