Hi I need help with this.

"En güvendiği insan tarafından sırtından bıçaklanır..."

Does this mean "someone he/she trusts the most is stabbed in the back?" Or "she/he will be stabbed by someone he/she trusts the most."

Thank you 

It means;

´He is stabbed in the back by the person he/she most trusts...´ (It is in "geniş zaman")

To exactly understand the meaning you must proivde the complete sentence...maybe it tells about past maybe future...

Best.

The whole sentence was this: Hiç beklemediği bir şey olur. En güvendiği insan tarafından sırtından bıçaklanır...

So yeah, your translation makes a lot of sense. Thank you 

Something he/she was no expecting at all happens. He/she is stapped in the back by the one he/she most trusts.

To understand he or she, all of the story must be known

No problem.