They dont actually know whats coming and where - will it be a sweep down from Kharkiv behind the lines to Bhakmut and wipe out all of Wagnar? Will it be clear down to Melitopol and trap and entire army before heading to Crimea? Could all of Donetsk be retaken down to Mariupol in a blitzkrieg motion?
There are a lot of factors we might not have visibility on which might make a difference i.e. if ammo is running out in one sector and they need to relieve the pressure by attacking elsewhere, etc. but I think the most likely indicators will be where Russian troops are least tested and/or least experienced troops are deployed and where it will most likely precipitate a general collapse of the Russian defences. Though going hard at the Kherson direction and putting Crimea at threat is probably the most likely way to drain Russian forces from other sectors making the wider job of the Ukrainian army easier.