Someone would have to give this person an actual Marketo account.
There are some good public resources, but no free accounts.
Marketo is taught at a college in San Luis Obispo, CA and I assume they use some sort of demo account. Perhaps there's a way your friend could take the course that Cal Poly offers if they give an online version?
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Also note that docs.marketo.com is entirely open and free to read/consume.