Thank you for reaching out to the community and sorry for the wait!
May I ask, what kind of complications does your friend have? Is his asylum procedure already finished (what is his current legal status)?
You can read more about the necessary requirements for marriage in the NL on the following website: https://www.government.nl/topics/marriage-cohabitation-agreement-registered-partnership/question-and-answer/marrying-a-foreign-national-in-the-netherlands
On the website it states: "...if you are not a Dutch national you must have a residence permit or a completed personal declaration." (residence permit doesn't apply to EU or EEA nationals though). It further shows that you are unable to get married if both of you live abroad and neither you nor your partner is Dutch.
So considering the research and similar cases here on Wefugees, it looks like your friend would need to get married in the country he applied for asylum - which is Germany in his case.
The duration of the marriage procedure in Germany highly depends on how long it takes to gather the required documents. Here are some similar questions and answers that provide more information: https://www.wefugees.de/801506/like-learn-more-about-the-marriage-procedure-germany-refugee
Also have a look at this link from the Wefugees Blog - scroll down for the English version on how to get married in Germany: https://wefugees.wordpress.com/2018/04/20/heiraten-in-deutschland-how-to-marry/
I hope that I could answer your question, definitely have a look at the other threads or the Blog article for more information on marriage in Germany. You can still get back to me with the information I asked for and we can have another look.
All the best,