You can meet Officer Effiong if you've unlocked the Gym by advancing your relationship with Bob. You can't unlock the gym this way if Bob is evil in your playthrough. Instead, check out the alternate unlock method on the Gym page.
Once you've unlocked the Gym, here's what you can do with Officer Effiong.
After you have smuggled AIKO out of the building via the huge plug, you would have met the security guard Effiong. Anytime you're at the gym afterwards and heading to the showers, there is a random chance that you'll run into Effiong. She'll ask you if you could spot her, you can either [hurry over to help] her or say [you don't have time right now].
If you help her you'll act as her spotter and get some different text depending on how high your strength currently is.
If you say you can't help right now it will make this event repeat again some time in the future randomly again.
After she finishes her workout, you both will head to the showers where she'll ask if you can wash her back. You can accept or decline. Accepting will move you forward to the next scene.
After finishing with her back, she'll turn around and you'll be able to choose what lower bits she has:
[That's... that's a penis!]
This will set her as a female with a penis
[That's... that's a penis! And a vagina...]
This will set her as a futa with both a penis and vagina
[Woah, cyber-cock!]
This will set her as a female with a cybernetic penis
[Woah, cyber-cock upgrade for dual-threat!]
This will set her as a cyber-futa with both a penis and vagina
[How does she have muscle definition around her labia?]
This will set her as a female with a vagina
When you finish washing her, she'll return the favor then she'll get changed and leave. Once she's gone you'll get changed too and get ready to leave.
After working out with Effiong on the weekend, she'll head over to a private shower where you can choose to either ask if she want's a personal wash down, or hit the shower yourself and leave.
If you choose to join her, you'll both head into the private shower where you'll get many options in what you want to do with her.
There are no skill checks for the sex but how you have sex will depend on how you set her "lower bits" in the previous event.