Diaa,
PMI has an FAQ on their website in which they answer many questions at
www.pmi.org/Certification/Certification-FAQ.aspx#audit
. The closes I found to your situation is this here:
A supervising manager is no longer at the company. How can this project be verified?
The supervising manager can still verify although they are not at the company. If this option is not feasible, a colleague from the project can verify, or a current manager or supervisor, who has intimate knowledge of the project, can verify.
In my opinion, this applies to your situation as well. So since your direct manager is on vacation it should be possible for the site manager to verify. However, please contact PMI quickly to verify that this is the case:
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