If you know the line number, then you can use tokenat(text, lineNumber, newline) expression.
Otherwise you will have to somehow identify the beginning and end position in the text. For example if the line begins with some tag, then you can use find() to find this tag and them mid() to extract the text.
See the documentation:
construct.net/en/make-games/manuals/construct-3/system-reference/system-expressions