There’s something about dining out that feels like a communal experience. You’re all there together, eating from the same menu, interacting with the same servers. But unless you’re actually sitting at the same table as other guests, I think it’s safe to assume that people generally expect to be left to their dining companions and their meal. (I certainly do, don’t you?)
So when it comes to asking another table if they like what they ordered, I’d say you need to read the room. Yes, you might be really curious about the caviar gnocchi or the uni soba, but if the table beside you is a couple clearly out on a date, or in the middle of a deep conversation, or a group of friends catching up, maybe it’s best if you don’t interrupt to see if they’re enjoying their meal. It could be misconstrued as rude if you do.
On the other hand (and can you tell I’m not a super-gregarious diner?), if you’re already engaged in a conversation with a neighboring table and no one seems to mind this, continuing the conversation throughout the meal to see if they liked what they ordered seems totally reasonable and maybe even welcome considering you’re already somewhat acquainted.
If you’re desperate to know how a dish is and don’t want to bother other guests, you could always ask the server for their honest feedback, noting any personal preferences you have that might help you decide if you’ll like something or not.