When writing "1 week 3 days," if week is abbreviated to wk., should days also be abbreviated? If so, what should it be abbreviated to?
The abbreviation for day is "d".
This abbreviation is rarely used, however is considered acceptable in certain contexts, one being when used in conjunction with other time abbreviations.
I think the answer is yes, that for consistency, you should abbreviate both. However, it might make more sense to write is as "10 days", depending on the context.