Q. 1. Can a Catholic be excommunicated from the Church without knowing it?
A. 1. According to the Code of Canon Law, # 1323.2 a person cannot be excommunited if he/she does not know that he/she has violated a Catholic Church teaching that results in excommunication.
Below is the Code of Canon Law for your reference:
"Canon Law # 1323 - The following are not subject to a penalty when they have violated a law or precept:
1/ a person who has not yet completed the sixteenth year of age;
2/ a person who without negligence was ignorant that he or she violated a law or precept; inadvertence and error are equivalent to ignorance;
3/ a person who acted due to physical force or a chance occurrence which the person could not foresee or, if foreseen, avoid;
4/ a person who acted coerced by grave fear, even if only relatively grave, or due to necessity or grave inconvenience unless the act is intrinsically evil or tends to the harm of souls;
5/ a person who acted with due moderation against an unjust aggressor for the sake of legitimate self defense or defense of another;
6/ a person who lacked the use of reason, without prejudice to the prescripts of cann. ? 1324, §1, n. 2 and ? 1325;
7/ a person who without negligence thought that one of the circumstances mentioned in nn. 4 or 5 was present."