TYPO3 Core

SOLUTION

Bind a "current" argument to the ViewHelper to provide the ContentObject UID.

In ClickEnlargeViewHelper.php

Add

$this->registerArgument('current', 'integer', 'The Content Object UID', false);

To the initializeArguments() function.

Then add this to the renderStatic() function:

if (isset($arguments['current'])) {
            self::getContentObjectRenderer()->setCurrentVal($arguments['current']);
        }

Now call the ViewHelper like this:

<ce:link.clickEnlarge image="{column.media}" configuration="{settings.media.popup}" current="{data.uid}">

And change the constant to lightbox[{current}]

Sorry I'm not familiar with Gerrit, yet. Hope someone else can push this to Gerrit...
The argument "current" in the ViewHelper maybe also should be renamed to "contentObjectUid"

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/48406

Patch set 3 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/48406

Patch set 4 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/48406

Patch set 5 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/48406

The problem still exists in the current master branch. IMO the problem should be fixed for 8.7 LTS, since grouping of lightbox images is currently broken in Fluid Styled Content. The existing patch contains breaking changes, so maybe it is better to fix the bug with non-breaking changes.

Is it real a bug of "fluid_styled_content"? And not a bug of fluid?
With "field:uid" I should get the id of the content element. But i get the id of the page.

I get the following results:
"field:uid" - id of the page, should get the id of the element
"field:pid" - id of the parent page, should get the id of the page
"field:header" - nothing, should get the headline
"page:uid" - id of the page - right
"page:pid" - id of the parent page - right
"page:title" - page title - right

TypoScript to the rescue! Here's a workaround for TYPO3 8.7:

lib.contentElement.variables.10 = LOAD_REGISTER
lib.contentElement.variables.10.content_uid = TEXT
lib.contentElement.variables.10.content_uid.field = uid
lib.contentElement.settings.media.popup.linkParams.ATagParams.dataWrap = class="{$styles.content.textmedia.linkWrap.lightboxCssClass}" rel="{$styles.content.textmedia.linkWrap.lightboxRelAttribute}[{register:content_uid}]" 
lib.contentElement.stdWrap.append = RESTORE_REGISTER

The solution is:

lib.fluidContent.settings.media.popup.linkParams.ATagParams.dataWrap = class="lightbox" rel="lightbox[{file:current:uid_foreign}]" 

{file:current:uid_foreign} gives the id of content element.

See also: https://forum.typo3.org/index.php?t=rview&goto=753239#msg_753239