New International Version
(He did not know what to say, they were so frightened.)

American Standard Version
For he knew not what to answer; for they became sore afraid.

Berean Study Bible
For they were all so terrified that Peter did not know what else to say.

Douay-Rheims Bible
For he knew not what he said: for they were struck with fear.

English Revised Version
For he wist not what to answer; for they became sore afraid.

King James Bible
For he wist not what to say; for they were sore afraid.

World English Bible
For he didn't know what to say, for they were very afraid.

Young's Literal Translation
for he was not knowing what he might say, for they were greatly afraid.

Mark 9:6 Additional Translations ...