君の言うことは

what you say

→ 君
phrase Uncommon #10,511
what you say 君の means “your,” and 言うこと refers to what someone says or means. 君 is an informal way to say “you,” often used toward someone of equal or lower status. は marks the topic: “as for what you say...”
JA: 君の言うことはよくわかるよ。
EN: I understand what you’re saying.

君の言うことはいつも正しい

You're always right.

君の言うことは全く理解することができない

I can't understand a word you're saying.

この見地からすると君の言うことは正しい

From this perspective, what you say is correct.

君の言うことはまったく的はずれ

What you're saying is completely beside the point.

君の言うことは極端じゃないか

Aren’t you being a little extreme?

たとえ君が何と言おうと君の言うことは信じない

No matter what you say, I won't believe you.

君の言うことは僕が彼から聞いたこととは全く違う

What you're saying is completely different from what I heard from him.

君の言うことは全く分からない

I don't understand a word you're saying.

君の言うことは問題にならない

What you say doesn't matter.

君の言うことは信じがたい

What you’re saying is hard to believe.

君の言うことは正しい

What you’re saying is right.