RIDDLE 1 - This question can only be answered from an unusual perspective. Can you get yourself there?
Gadgets used: Batclaw
In order to solve this riddle, you will first have to start climbing the Wonder Tower. Stop after reaching one of the higher levels, at the spot from which you can reach the second northern extension arm #1. If you now turn around and activate the Detective Mode, you should note an incomplete question mark painted on the tower #2.
Don't waste time on searching for the missing dot, as it's impossible from this position. Instead, use the Grapnel Gun to reach the upper floor (the one with the control panel) #1. After getting there, turn around and stand by the ledge #2.
You need to jump off the ledge and glide north. After flying a couple dozen meters, start turning around and try to reach a position from which you will see the whole question mark (screen above). Don't worry if you don't manage to do it on the first try, as you can always return to the starting point and start all over again. What's more, if Batman crashes against something and falls down, the game will automatically return him onto one of the previous ledges.
Notice! If you can't handle solving this riddle by gliding, you can always use the alternative method implying standing on the mentioned northern extension arm #1 and afterwards jumping off it (B button), trying to scan the question mark in mid-air #2.
RIDDLE 2 - Where can you get a wonderful view of the past?
Get onto the big terrace after riding the elevator to the upper level of the Tower and scan the Gotham City painting (screen above).
RIDDLE 3 - Crime is a global issue. You'll never stop it, Batman.
Stand beside the antique monument with a globe connected with the Wonder City (screen above) and scan it.
RIDDLE 4 - Read all about it! Is this the sign of the Times?
Find the plate informing of the shutdown of Wonder City (screen above) and scan it.
RIDDLE 5 - Wanted: Dead... and alive?
Find the overturned Solomon Grundy wanted poster (screen above) and scan it.
RIDDLE 6 - Do these demonic twins pose a threat?
Grab the twins statues in one frame (screen above) and scan it.