The 'forgetting curve' is a concept that was developed by the German psychologist Hermann Ebbinghaus in the late 19th century. It triggered a series of more studies on the topic of memory loss over time. Ebbinghaus found out that memory retention declines at an exponential rate over time if there is no active effort to retain it.
What does this mean for the area of learning? If you are attending a two-day training and you don't engage in active retention afterwards, you are likely to lose approximately 90% of what you have learned within one month. In order to avoid this, here is what I usually do:
Make clear what your own personal learning targets are before even joining the training.
Write your own summary of the key concepts from the training. You can put the names of the concepts in a mind map on which you also show connections between the different concepts. Then integrate the summaries of the concepts on the lower branches of the mind map or write one separate summary paper card for each concept with the most relevant information.
Repeat & test yourself on your newly attained knowledge every couple of days after the training. You can e.g. do this by joining forces with another colleague from the training to ask yourselves mutually (based on the summary cards) about certain concepts. If you don't have a partner, just read the key concept's title and try to remember the details.
Make sure that the training content is relevant to your daily tasks and reflect on how you can apply what you have learned. Make sure to start with the ideas that will likely have the biggest impact and take small steps.
Work with mnemo techniques like visualization of abstract concepts in mind maps.
What are the strategies that you will try to fight the forgetting curve after your next training?