Can you upstage comedy targeting an already readied unit? And is it possible to repeat upstage comedy targeting twice a single unit, just to proc the legend?

Yes, you can target an already-readied unit with Upstage Comedy, and you can target the same unit twice if you pay the Repeat cost. However, because a unit that is already readied cannot be readied again, targeting the same unit a second time will not trigger "when you ready" effects for that second instance.

1. Targeting an already-readied unit

An already-readied unit is a legal target for Upstage Comedy.

According to Rule 415.1.c, "If a Unit is instructed to be Readied while it is already Ready, nothing additional happens." Targeting a unit does not require that the effect will successfully change the unit's state—only that the unit meets the definition of the target. By analogy to RiftJudge FAQ #7700 (which confirms stunned units are legal targets for stun effects), targeting a unit with an effect it is already in the state of is permitted.

2. Repeating and targeting the same unit

You may target the same unit twice when using Repeat, as targets for the repeated instance are chosen independently (per Rule 820.2.a and RiftJudge FAQs #9078 and #88).

However, per Rule 415.1.b, "A Unit that is already Ready cannot be Readied again." Because the second instance of the effect fails to change the unit's state, it will not trigger any abilities that specify "When you ready a unit."

Note: I could not fully verify this ruling against the retrieved rules.