I think you're not getting any answers because the question is very unclear.
Unless I'm missing something, the only way to determine the genotype is to look at what is reported in the "Tumor_Seq_Allele1" and "Tumor_Seq_Allele2" columns of your MAF file.
Having said this, I'm confused as to why you have not considered looking at the allele columns and I'm even more confused as to how you could use dbSNP in any way to determine the genotype of your snps, so I may be misunderstanding what you are looking for.
what did you try so far ?
It helps to see some of the data in addition to the header line.
@Pierre I tried dbsnp but it is tedious for large data.
MYPN 84665 broad.mit.edu 37 chr10 69933969 69933969 + Missense_Mutation SNP G A A rs7916821 by-cluster,by-frequency,by-2hit-2allele,by-hapmap,by-1000genomes normal normal Unknown Unknown Unknown Phase_I Capture Illumina_GAIIx g.chr10:69933969G>A NM_032578.2 + c.2120G>A c.(2119-2121)AGT>AAT p.S707N NP_115967.2 None None None None 0 --- --- 0