Getting this information for GISTIC2
Depends on the software to generate the segmentation file;

For example I have used scatngs for segmentation that for sample returns 

Segment number
Chromosome
Start position (origin-1)
End position (origin-1)
Major copy number—normal
Minor copy number—normal
Major copy number—tumor
Minor copy number—tumor


By  log2(Major copy number—tumor +  Minor copy number—tumor /ploidy of each sample) you would get segment mean

For number of probes 

The number of probes depends on where the data came from.
1) From SNP arrays:  Number of array probes within each segment.
2) From exon capture data:   Probes are the ends of exons and so the number of probes are equal to the number of exons  X 2.
3) From whole genome sequencing:  Probes are the boundaries of bins used to generate the copy number data and so the number of probes are equal to the number of bins + 


For example in my case for scatngs

Each SNP is a marker, and so you have to count how many of these SNPs are on each segment


I have asked this question in 

Extracting the number SNP in each range