The manuscript that you mention should list precisely how the clinical information was obtained. I have just checked and it states:
The raw mRNA expression data and the corresponding clinical
information, which was available for 487 GBM samples, were downloaded
from the Cancer Genome Atlas (TCGA) database
The URL does not even work.
In Figure 5 of the manuscript, they relate to overall and disease-free survival, but it is not explicitly stated which parameters they used from the TCGA.
As it's not clear, I would reach out to the authors of the manuscript to find out the exact parameters that were used. The TCGA clinical data is vast and there are many different clinical variables that they could have used (multiple survival variables exist). One can normally download the clinical data from the GDC Legacy Archive.