EDI files or their JSON representation are automatically validated when you hit any of the translation buttons. You can't trigger the validation on its own.
The validation process checks for any inaccuracies when the contents are matched to the rules of the standard (or your own rules if using a custom model). If any were found, they are reported as:
When translation has failed, as OperationResult object at the bottom of the JSON Editor.
When validation has failed, as highlighted error icons in the EDI Editor. You can hover over any of the red icons for details.
When a secondary model was used for translation, as highlighted warning icons in the EDI Editor. You can hover over any of the orange icons for details.