Answer
The quark makeup of the antiproton is $\bar{u} \bar{u} \bar{d}$
Work Step by Step
The quark makeup of the proton is $uud$
We can verify that the quark makeup of the antiproton is $\bar{u} \bar{u} \bar{d}$
The antiproton $\bar{p}$ has charge $-1$, strangeness $0$, and baryon number $-1$
The antiquark $\bar{u}$ has charge $-\frac{2}{3}$, strangeness $0$, and baryon number $-\frac{1}{3}$
The antiquark $\bar{d}$ has charge $+\frac{1}{3}$, strangeness $0$, and baryon number $-\frac{1}{3}$
The conservation laws show that the quark makeup of the antiproton is $\bar{u} \bar{u} \bar{d}$.
