The sequence is as follow:
$S+1=T$
$T+1=U$
$U+1=V$ (the first alphabet is increment by 1from LHS side)
$C+2=E$
$E+2=G$
$G+2=I$ (the second alphabet is increment by 2)
$D+2=F$
$F+2=G$
$G+2=J$ (the third alphabet is increment by 2)
so the missing term is $VIJ.$