If you want to quickly check classifications jobs before finishing all iterations, here's a quick way to do so.
First, open up relion GUI session and follow the screenshot to open up Display dialog.
Second, go to the specific classification job folder and choose the _model.star file with specific iteration that you want to examine.
Lastly, make sure to check "Sort images on rlnClassDistribution" and "Reverse sort?" to display most populated classes come first descending order so that you can easily tell whether the classification is working or not.
Here's a portion of the display output window.
Hope this helps you examine whether your classification is heading towards right direction.