Nevermind, i had to use escape quotes.
(defun c:stv ()
(setq lst (cd:DWG_GetCustomProp(cd:ACX_ADoc) ))
(setq url (strcat "\"https://www.google.com/maps/@?api=1&map_action=pano&viewpoint="(CDR (assoc "LATITUDE" lst))","(CDR (assoc "LONGITUDE" lst))"&heading=0&pitch=0&fov=100\""))
(startapp "explorer" url)
(princ)
)