M.2 SSDs can be SATA or PCIe devices. The adapter you'll need depends on which protocol you have. You can usually determine what type it is by the labeling, but it would be best to search for the model number for verification.
The drive's label will usually show text similar to "PCIe GenX".
You will need a PCIe write blocker and an M.2 PCIe Adapter:
A1510 - PCIe M.2 SSD Adapter (TDA7-2) - https://digitalintelligence.com/store/products/a1510
The drive's label will usually have a "Serial ATA" emblem on it and may have the text "SATA".
You will need a SATA write blocker and an M.2 SATA Adapter:
A4710 - mSATA and M.2 to SATA Adapter Kit - https://digitalintelligence.com/store/products/a4710
A4720 - mSATA/M.2 SATA SSD Adapter (TDA3-3) - https://digitalintelligence.com/store/products/tda3-3-msata-m-2-sata-ssd-adapter
NVMe SSDs can be encrypted, one of the popular schemes is OPAL which will have the text "OPAL" on the label.
Currently, the only write-block device that can detect OPAL is the TX1 Forensic Imager:
Recently there have been new encryption schemes released called Opalite and Pyrite, which are subsets of the OPAL self-encrypting standard. Currently the TX1 does not support these subsets.