Lentils and stuff to make a broth...

[Mysaucepansdontmatch]

I have had a broth mix soaking in cold water.

For about four days.

Is it still safe to cook with?

Packet says soak overnight

Rinse very thoroughly.
Boil rapidly for 10 mins.
Drain that water and then follow instructions on packet with fresh water.

It may have started to sprout or ferment after that length of time. I'd chuck it.