Of course they don't understand what they talk 有一处错误请改正
问题描述：
Of course they don't understand what they talk 有一处错误请改正
答
后半句时态有问题，改成现在进行时 或 过去式 都可以。
Of course they don't understand what they are talking.（当然他们不明白他们正在所谈的内容。）
or
Of course they don't understand what they talked.（当然他们不明白他们所谈到的内容。）
答
of course they don't understand what they talk ABOUT.