Agree with TYN, but the sense is clear, in informal speech, if you leave it out (or replace it with "if". But "whether" is better because it's clearer imho.)
Tes yeux noirs
Wed 2 Sep, 2015 03:47 pm
Tes, tho smart as can be, gets involved with technicalities
These foreign learners are not asking if some way of saying something would be OK to say to the good ol' boys who chew the fat down at the trucker's bar in East Jesus, Oklahoma, they are asking about what they think of as "proper English". It therefore behoves us to answer accordingly.