I believe you can get that info from the Guest Services desk onboard (I know there is a sheet with the recommended tipping amounts that they use for when you charge your tips). I am sure they would give you a sheet even if you planned on paying in cash.
We always like to have the amount set aside even before we sail. We bring the tip money in a separate envelope and keep it in the safe until it is time to put in the individual envelopes that DCL provides.
The suggested tipping amounts are printed in the DCL Stateroom books that you'll find in your stateroom. They are also given out with the tip envelopes, near the end of your cruise.
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