How can I Film Inconspicuously with a DSLR?
Any wireless microphone kit would work. Of course the more you spend the more reliable kit you will get. Wireless mic kits under US$500 are typically cheap, fiddly, unreliable, disposable plastic toys.

There are "right angle spy lens" adapters that screw on to the front of the lens and allow you to shoot to the side. So it is not obvious that you are shooting them.  They are quite inexpensive and available at the usual larger online shops.



That said, in most of the civilized world, it is illegal to use the recognizable likeness of anyone without their written consent.  And additionally, it is typically against the rules to shoot on private property (like a shopping mall) without written authority of the management. You are quite likely to get expelled or even arrested for trespassing if you try this in any kind of a mall with half-decent security forces.