Something my team started recently that we rather like is to put together a Kanban-style board (Trello would be perfect for this - we used Taiga as the tool had

Something my team started recently that we rather like is to put together a Kanban-style board (Trello would be perfect for this - we used Taiga as the tool had to be in-house) with cards like "How do I do build X?" and "How do I troubleshoot Y" that have links to our Wiki pages that cover the relevant topics. New team members go through the board moving cards from "New" to "Done" as they research/answer the questions. In theory, once they're done, they should know all the major information needed to do their jobs. This is a win in both directions as it also forces us to write high-quality documentation. If the person gets stuck, they generally have a good idea who to bug (the most recent author of the page) for clarification. For a first employee in that particular space, it would be a valuable exercise for them to start building that deck and the associated documentation. It might make the "time to first code contribution" take a little longer, but should pay dividends in reducing mistakes.