Derek wrote:

How do Jehovah's Witnesses interpret the following scripture?

Ex. 21:20-21 says, "If a man beats his male or female slave with a rod
and
the slave dies as a direct result, he must be punished, but he is not to
be
punished if the slave gets up after a day or two, since the slave is his
property."

Was this a directive from Jehovah?

It was called the Law of Moses

Slave could be flogged by master (Ex 21:20, 21) If maimed, was given
freedom. (Ex 21:26, 27) If slave died under his master’s beating, master
could be punished by death; judges would decide the penalty (Ex 21:20; Le
24:17)

The Law protected slaves from brutalities. A slave was to be set at
liberty if mistreatment by the master resulted in the loss of a tooth or
an eye. As the usual value for a slave was 30 shekels (compare Ex 21:32),
his liberation would have meant considerable loss to the master and,
therefore, would have served as a strong deterrent against abuse. Although
a master could beat his slave, the slave, depending upon the decision of
the judges, was to be avenged if he died under his master’s beating.
However, if the slave lingered on for a day or two before dying—this
indicating that the master had not intended to kill the slave but to
discipline him—he was not to be avenged. (Ex 21:20, 21, 26, 27; Le 24:17)
Also, it would appear that for the master to have been considered free of
guilt the beating could not have been administered with a lethal
instrument, as that would have signified intent to kill. (Compare Nu
35:16-18.) Therefore, if a slave lingered on for a day or two, there would
be reasonable question as to whether the death resulted from the
chastisement. A beating with a rod, for example, would not normally be
fatal, as is shown by the statement at Proverbs 23:13: “Do not hold back
discipline from the mere boy. In case you beat him with the rod, he will
not die.”

Certain privileges were granted to slaves by the terms of the Law. As all
male slaves were circumcised (Ex 12:44; compare Ge 17:12), they could eat
the Passover, and slaves of the priest could eat holy things. (Ex 12:43,
44; Le 22:10, 11) Slaves were exempted from working on the Sabbath. (Ex
20:10; De 5:14) During the Sabbath year they were entitled to eat of the
growth from spilled kernels and from the unpruned vine. (Le 25:5, 6) They
were to share in the rejoicing associated with the sacrificing at the
sanctuary and the celebration of the festivals.—De 12:12; 16:11, 14.