You can use parted -l to determine the type of partition table. Eg:

$ sudo parted -l

Model: ATA TOSHIBA THNSNS25 (scsi)

Disk /dev/sda: 256GB

Sector size (logical/physical): 512B/512B

Partition Table: msdos

Number Start End Size Type File system Flags

1 4194kB 32.2GB 32.2GB primary ext4 boot

2 32.2GB 256GB 224GB primary ext4

https://unix.stackexchange.com/questions/120221/gpt-or-mbr-how-do-i-know