[Plugin: Events Manager] Show location/booking form in sidebar/widget

You can do that by creating single-event.php in your theme and using placeholders e.g. https://www.ads-software.com/support/topic/events-manager-eventslocation-pages-cant-get-sidebar

https://wp-events-plugin.com/documentation/placeholders/

But how can I use the placeholders inside widgets?

sorry.

for location or events, you can simply use EM Location widgets or Events widget but adding booking form in widgets is not possible at the moment without coding on your part.

Coding is not a big problem. But where to start? ??

you can start by creating single-event.php or see my posted link above.