Which quote or lyric from the song "Sick Boy" by The Chainsmokers would best go with the idea of struggling with self-identity?

Different listeners are going to react differently to this song, and different listeners are going to pick different lines that "best go with the idea of struggling with self-identity." Feel free to pick which lyric resonates best with you and explain why you chose that lyric.
As a song from an electronic dance music (EDM) group, "Sick Boy" is an incredible song because of how different it is from the songs typical of the genre. More often than not, EDM songs are all about feeling good in the moment. There are heavy elements of individualism, love, and carpe diem. Jonas Blue's "Hey Mama" is a good example because the chorus specifically mentions not wanting to wait. It's all about seizing the moment.

Don't wanna wake up one day wishing that we'd done moreI wanna live fast and never look back, that's what we here forDon't wanna wake up one day wondering "Where'd it all go?"'Cause we'll be home before we know, I wanna hear you sing it

The Chainsmokers themselves are guilty of this kind of songwriting as well. Their song "Roses" is all about love and living in the moment.

We could waste the night with an old filmSmoke a little weed on the couch in the backroomHideawaySay you'll never let me go

Even the incredibly repetitive song "Are You With Me" by Lost Frequencies manages to emphasize the importance of living life to the fullest with a possible romantic interest.

I wanna dance by water 'neath the Mexican skyDrink some Margaritas by a string of blue lightsListen to the Mariachi play at midnightAre you with me, are you with me?

Knowing that the genre is generally all about feeling good, it is amazing that The Chainsmokers would produce a song like "Sick Boy." The song itself is quite depressing because it is not ashamed of pointing out negative aspects of society. The song definitely speaks out against narcissism, and it highlights potential dangers of social media and not having a strong sense of self-identity.
I think the best line that goes with the idea of struggling with self-identity is the line that questions how many "likes" a person's life is worth.

How many likes is my life worth?

This line clearly equates a person's value with likes/clicks/thumbs-ups on some kind of social media. That's a scary thought to know that someone could determine their self-worth from that kind of feedback. What this then encourages is people presenting themselves in a way that will gain the most likes. This will not likely be reality. The person will be creating a false self-identity in order to find self-value. In other words, the "real" person is worthless. The created image is worth more. Who I am doesn't matter. Who I am to all of my followers is what matters. That is a warped sense of self-identity, and the song points out the danger of it in the following lines.

Make no mistake, I live in a prisonThat I built myself, it is my religion

The false self-identity being created to determine value is a self-built prison. Notice that the lyrics say "prison" instead of something like "palace." The negative connotation is clear. The "religion" reference is interesting too because it makes a listener see how all of this narcissistic love of a false image is essentially a form of worship of the self.
https://edm.com/features/timeless-tracks-that-hit-right-in-the-feels