I think you want to convert the result from the NeighborFinder, which is probably a list, to attributes?

The question is, how do you want the result look like. One way to do this is to concatenate the results of the listelements into one attribute. ListConcatenator can do this.

Another way is to do this manually, using an AttributeCreator, create an attribute with name ClosestPoint0 and a value of _closest_candidates_list{0}.PointId.

An alternative is to explode the list into features and handle it that way. ListExploder.

Attached a sample workspace demonstrating some of this.

To add to @nielsgerrits answer, there is also a Hub transformer called the ListBreaker that will convert a list of values into separate attributes. If handling the list is the source of the problem, this may be another solution.