%%%%%%%%%%@yahoo.com
%%%%%%@wanadoo.fr
%%%%raviplywoodglasscentre@yahoo.comravi
%%nameemail%%@yahoo.com
%.getincontact@numberland.com
%0dronbracale@roadrunner.com
%1%3@example.com
%1@elsewhere.com
%1@example.com

{"email":"%%%%%%%%%%@yahoo.com"}
{"email":"%%%%%%@wanadoo.fr"}
{"email":"%%%%raviplywoodglasscentre@yahoo.comravi"}
{"email":"%%nameemail%%@yahoo.com"}

awk '{ printf("{"email":"%s"}", $l);}' test

$ sed 's/.*/{"email:"&"}/' file
{"email:"%%%%%%%%%%@yahoo.com"}
{"email:"%%%%%%@wanadoo.fr"}
{"email:"%%%%raviplywoodglasscentre@yahoo.comravi"}
{"email:"%%nameemail%%@yahoo.com"}
{"email:"%.getincontact@numberland.com"}
{"email:"%0dronbracale@roadrunner.com"}
{"email:"%1%3@example.com"}
{"email:"%1@elsewhere.com"}
{"email:"%1@example.com"}

sed -i 's/.*/{"email:"&"}/' *

sed -i.old 's/.*/{"email:"&"}/' *

awk -v format='{"email":"%s"}n' '{printf format, $1}

sed -e 's/(.*)/{"email":"1"}/g' a.txt