I didn't know what to do

I didn't know what to do first.

Je ne savais pas quoi faire en premier.

I didn't know what to do with it.

Je ne savais pas quoi en faire.

I didn't know what to do then.

Je ne savais pas quoi faire à ce moment-là.

I was so indignant, I didn't know what to do.

J’étais tellement indigné que je ne savais pas quoi faire.

— The Irony of Fate, or Enjoy Your Bath! (1976)

I didn't know what to do.

Je ne savais pas quoi faire.

— Don Juan DeMarco (1994)

I didn't know what to do to shut them up.

Je ne savais pas quoi faire pour les faire taire.

Since I didn't know what to do, I asked him for advice.

Comme je ne savais pas quoi faire, je lui ai demandé conseil.

The last time that happened I didn't know what to do.

La dernière fois que c’est arrivé, je ne savais pas quoi faire.

I didn't know what to do when Tom told me that.

Je ne savais pas quoi faire quand Tom m’a dit ça.