私は彼の言ったことが

I ... what he said

→ 私
phrase Rare #24,226
I ... what he said This is an incomplete sentence pattern: 私は means “as for me,” and 彼の言ったこと means “what he said.” It is typically followed by a verb such as わかる or 理解する, meaning that the speaker understands or does not understand what he said.
JA: 私は彼の言ったことがよくわかりました。
EN: I understood what he said well.

私は彼の言ったことが信じられなかった

I couldn't believe what he said.

私は彼の言ったことが本当かどうか確かめるつもりだ

I intend to find out whether what he said is true.

私は彼の言ったことがわからなかった

I didn't understand what he said.

私は彼の言ったことが少しも理解できない

I can't understand anything he said.

私は彼の言ったことが聞き取れなかった

I couldn't make out what he said.