If we ask our higher self just before going to sleep to show us important past life trainings and inspirational experiences, can it help us recall such things and even retain the memory when we wake up?

This is quite possible to do. The success will vary from individual to individual but this is often a means of conveying inspiration and guidance, to impart it during the dream state and then have the person recall it on their own once they wake up in the morning, so this is a well-worn path and will work for people more than not. There can be constraints depending on the nature of the inquiry and its alignment with what is highest and best for the individual, as well as whether or not it creates inner conflict in some regard wanting to recall something that the deep subconscious wants to be off-limits or has been programmed to make it so. But, in general, this is a fine way to further the being and help utilize all prior knowledge and awareness more effectively.