In Bitcoin Core, the scriptWitness property (for the CTxIn class) is serialized from a CTransaction as a std::vector<std::vector<unsigned char> >, so I would imagine the serialized version would look something like:

TxWitness:

+------------+-------------------------+------------------------+
| Field Size |        Description      |       Data Type        |
+------------+-------------------------+------------------------+
| 0+         | witness_component count | var_int                |
| ?          | witness_components      | witness_component[]    |
+------------+-------------------------+------------------------+

WitnessComponent:

+------------+------------------+-----------+
| Field Size |   Description    | Data Type |
+------------+------------------+-----------+
| 0+         | component length | var_int   |
| ?          | component        | uchar[]   |
+------------+------------------+-----------+

References:

• https://github.com/bitcoin/bitcoin/blob/master/src/primitives/transaction.h#L67
• https://github.com/bitcoin/bitcoin/blob/master/src/primitives/transaction.h#L254
• https://github.com/bitcoin/bitcoin/blob/master/src/script/script.h#L676