Below there is a summary of selected extra activities in Denny Park, specifically those, which may prove a bit problematic.
1) Mobile Command Center - Denny Park is a very small district, so you should not have much trouble finding the enemy base (it looks a bit different from the typical military construction which you encountered e.g. in the northern part of Seattle) or the Jammer located on the top of that, which should preferably be destroyed with a powerful missile fired from a distance.
After destroying the tower with a Turret, attack enemy forces. As usually in this type of situation, pay most attention to eliminating the elite opponents, while avoiding their powerful attacks. There are also several Auto-Turrets on the upper level of the base - it would be really nice to blow them up with distance attacks, so you did not have to worry about them later during the fight. You need to get to one of the higher levels of the central structure, and the easiest way to do that is by using Light Speed ??dash (Neon category). Start looking for generators mounted in the side supports of the local structure and destroy them, ultimately revealing the central core.
2) Blast Shards - Most of the shards are hidden on rooftops, but at this stage of the game you should already be acquainted with this. The only troublesome collectible is the one shown in the picture above, because the blue dot that stands for the location of the tracker drone may appear on the map with some delay (drone is attached to the neon billboard on Rexagon building, just by the roof of the skyscraper), namely after destroying one of the Jammers in neighboring Downtown district (the Jammer's range partly overlaps with ??Denny Park district).
3) Hidden Camera - The camera you seek is in the place shown in the above screenshot.
4) Audio Log - Once you start searching for the audio log, you need to get to the very top of the concrete structure standing by one of the crossroads. The hard disc lies in the place depicted in the screenshot.