Having grown up around the river, I can spot most (but not all wing dams) by changes in the surface of the water on a calm day. I've tried to show my wife what to watch for many times, but she doesn't see near what I can find. As a general rule, looking for straight lines in the water (typically 10 to 20 feet wide) that stretch in excess of 100 yards is a dead ringer for a submerged wing dam.
Now the confusing part. Just because you know they are there, doesn't mean a whole lot. Many wing dams will have a "break" or "access point" through which you can travel to reach sloughs or backwater areas. I've never seen anything official that tells where these "breaks" are. They are mainly found though watching "locals" traverse these lines in the water. You are safest to avoid them all together, but if you are like me, you'll find some reason you "need" to get to the other side (less wake, etc). I sit back on a busy day and watch multiple other boats pass through the area. Once I think I know what to do, I wait to see at least one boat that draws at least as much as I do then slowly and carefully duplicate what the others have done. So far, I haven't had any problems. Again you are safest to avoid these whenever possible.
Now to make things even more complicated. Just because to passed over a wing dam last week, or went through a "break" doesn't mean you can do it safely again this week if the water level has changed. During very low water, I've seen multiple wing dams that actually rise above the surface of the river by several feet. During high water, I've seen water get very swift and unpredictable near these "breaks".
Wing dams are typically "owned" by the Corps or Engineers and they are responsible for marking those hazards. Remember they are with the government and are hear to help you
You'll "sometimes" see channel markers that are positioned at the end of wing dams, but don't rely just on this.