The NationalMemo puts it this way:
Trump and his supporters have previously claimed that the Ukrainians did not know about the military hold, and thus there was no opportunity for extortion. Croft’s testimony rejects that claim, corroborating accounts from others, such as Laura Cooper, a high-ranking Pentagon official, that Ukrainian officials were not only aware of the hold, but worried about the ramifications of such a hold.
The LawfareBlog puts it this way:
Catherine Croft is a nine-year career Foreign Service officer currently serving as the special advisor for Ukraine negotiations. […] After Croft accepted her position advising Ambassador Volker in July 2019, she became aware for the first time that Volker and Rudy Giuliani were in contact.
[…] Croft noted that two individuals from the Ukrainian embassy in Washington, DC, contacted her about the hold. The two calls, Croft recounted, were roughly a week apart and were both before the August 28 Politico article that reported on the hold. She noted her surprise that the Ukrainians knew of the hold at that time––she felt they found out much earlier than she expected them to. According to Croft, the Ukrainians did not want the hold to become public because it “would be a really big deal, it would be a really big deal in Ukraine, and an expression of declining U.S. support for Ukraine.”
The actual Congressional questioning went like this:
Q: There was an August 29th Politico article talking about it. Do you remember if it had been public before then?
A: I think it was sort of known among the circles that do Ukraine security assistance, sort of gradually, as I said. From July 18 on it was sort of inevitable that it was eventually going to come out.
Q: I should correct myself, the article was on August 28th. Just for accuracy purposes, I’ll add that. And do you know if any Ukrainians knew about this or was this primarily U.S. officials?
A: Two individuals from the Ukrainian Embassy approached me quietly and in confidence to ask me about an OMB hold on Ukraine security assistance.
Q: And when was that?
A: I don’t have those dates.
Q: But it was before the August 28th time period, do you think?
A: I believe it was, yes.
Q: Okay. And these are—and what did you—what do you remember telling these folks?
A: I remember telling them that I was confident that any issues in process would get resolved. And I knew from my understanding of having worked with these individuals for a long time that they had no interest in this information getting out into the public.
Q: Okay. And did they call you together or was it two separate calls?
A: Two separate.
Q: Do you have an approximate estimation of how far apart these two conversations were?
A: With the two different Ukrainians? I thought it was roughly a week. But again, I can look up those dates and get back.
Q: Okay. And the last question is, whether you know the date or not of when it became public, do you remember it becoming public?
A: I honestly don’t specifically remember when it was reported in the public.
Q: But you remember at some point it became public?
A: Yes, yes, I do remember that.
Q: So do you recall how far before it became public you had these conversations, the second of the conversations?
A: I remember being very surprised at the effectiveness of my Ukrainian counterparts’ diplomatic tradecraft, as in to say they found out very early on or much earlier than I expected them to.
Q: In light of when it became public?
A: In light of when it became public.
The Questioner appears to be the Republican staff counsel Steve Castor, from the longer version of this Testimony (starting on page 86).
I find it hard to imagine that Sondland, or the Giuliani crew, did not make the withholding of aid threat “perfectly” clear, in their earlier communications with Ukrainian officials. They were pressuring Zelensky to “get with the Trump program” — not asking him to take it or leave it …
Take or leave … that “offer he could not refuse.”
Which means he had to have been told, otherwise Sondland wouldn’t have boasted, when directly asked by Trump, “So, he’s gonna do the investigation?” …
… “he’s gonna do it,” adding that President Zelenskyy will do “anything you ask him to.”
I was not aware until I read Ambassador Taylor’s testimony of the various exchanges on September 7-8 about President Trump apparently insisting that President Zelenskyy personally go to a microphone and say he was opening investigations of the Bidens and 2016 election interference, or Mr. Yermak’s message to Ambassador Sondland that President Zelenskyy was prepared to make a statement on CNN. However, Amabssador Taylor did tell me on September 8 “now they’re insisting Zelenskyy commit to the investigation in an interview with CNN.” I was surpriseD the requirement was so specific and concrete.
— David Holmes, Opening Statement to Congress.