\hline
Some text & \makecell{Some really \\ longer text} & Text text text \\
\hline
簡單說, 把想要換行的那一格, 用 \makecell{} 包起來, 需要換行的地方加上\\就可以了
記得使用 \usepackage{makecell}
ref
https://tex.stackexchange.com/questions/2441/how-to-add-a-forced-line-break-inside-a-table-cell