1. In Korean, the subtitle "아무것도 아닌 날" can be interpreted as 'An ordinary day,' but it also carries the double meaning of 'Someone of no importance.' Therefore, it can be understood as: 'Why Soae became interested in a worthless person like me (Sang-hyeon), even though I am a nobody.
2. Soae carefully observes the way he grips a can while in his 'Yoil' form, noting that it's identical to Sang-hyeon's habit. She also notices that he holds his chopsticks shorter than others, just as Sang-hyeon does. These subtle clues lead her to suspect that Yoil and Sang-hyeon might be the same person, or at the very least, that they are closely connected and know each other very well.
3. Given the manager's mention of a tight schedule with the PD, this episode is likely the final one for the trainees. It seems Group A and B are meant to select additional members who harmonize well with the fixed debut members (Won-jin and Izumi), while Group C is highly likely to be treated as a discard
Sorry if my English is a bit off, I'm using a translator.