The facts:
Giuliani admitted that the purpose of the meeting was to get dirt on Hillary Clinton. President Trump has also admitted this, and the Trump Junior e-mail chain makes that clear and undeniable.
Veselnitskaya was identified as a “Russian government attorney” in the emails released by Trump Jr, and one of the e-mails specifically said she would like to share some information about Clinton as “part of Russia and its government’s support for Mr. Trump.”
It’s not possible to declare with 100% certainty whether Giuliani is ignorant of the facts of the case or just plain lying. Given that he used to be a highly-respected attorney, I assume he is capable of proper preparation; given that Trump is basically his full-time job, he must have had plenty of time to assimilate at least the top-line facts of the Trump Tower meeting. Therefore, I assume he is lying.
(But I could be wrong. The fact that he USED to be a capable attorney doesn’t mean that he still is. 74 is not that old in today’s world, but he may nonetheless be experiencing some mental deterioration.)
The facts of the case show that Trump Junior took the meeting to get damaging information on Hillary Clinton from a person he fully understood to be a representative of the Russian government. It is possible to argue that such an action was not, per se, criminal, but it is not possible to deny the facts.