Here "cup" refers to what Jesus must suffer. Suffering is often referred to as drinking from a cup. AT: "drink the cup of suffering that I will drink" or "drink from the cup of suffering that I will drink from" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "baptism" and being baptized represent suffering. Just as water covers a person during baptism, suffering will overwhelm Jesus. AT: "endure the baptism of suffering which I will suffer" (See: [[rc://en/ta/man/translate/figs-metaphor]])