The key here is to use a special token, entity, which will allow us to chain the entities referenced one to the other from our token and to traverse them as for a small Sunday ballad. And because a drawing is better than a long speech, let us take a few examples.
We have a content (A) that references another content (B) with an Entity Reference field field_ref_content, and the content B contains an image, image referenced from field field_image. If we want to have the url of this image from the A content, we just need to use the following token: [node:field_ref_content:entity:field_image:entity:url]
We have a content (A) that references (field_ref_content) another content (B), the latter content references a paragraph (field_paragraph), paragraph to which an image is attached (the paragraph therefore references the image from field field_image). And we want to retrieve the image's url, from the content A. Our token to be used is then: [node:field_ref_content:entity:field_paragraph:entity:field_image:entity:url].
In the case of multiple fields it is of course necessary to target which entity to be accessed using its delta (or its index). For example, a content (A) that references paragraphs (multiple field field_paragraphs), paragraphs that have an image. To access the url of this image for the first paragraph (delta 0) we will then use the token: [node:field_paragraphs:0:entity:field_image:entity:url]
Finally, it is rather simple, no need here of a Drupal 8 expert. To access the values of a referenced entity, it is therefore enough to use the token entity and to associate it with the Entity Reference field used, and then we access the entirety of this entity and therefore its fields, and this in a recursive way, to infinity if needed.