The amino acid shown has $p{K}_a$ values 2.10 ($\alpha$-COOH), 3.90 (side-chain COOH) and 9.80 ($\alpha$-$\mathrm{NH}{}_3{}^{+}$). What is its isoelectric point?

The side chain is acidic, so the neutral zwitterion lies between the first two deprotonations: the species with net charge 0 is bounded by $p{K}_{a1}$ and $p{K}_{a2}$ (the two carboxyl groups), giving $\mathrm{pI}=(2.10+3.90)/2=3.00$. Averaging the last two values (6.85) or the first and last (5.95) uses the wrong pair. The amino acid is aspartic acid.