This lesson is about the several ways to say "or", but it is not exhaustive. Nevertheless, it will provide you what you need to know to understand how to express "or" correctly in Japanese.
The Adverbial Particle か
か can also list noun phrases to mean "or". それか starts a sentence with "or" in the affirmative and それとも starts a sentence with "or" in questioning. This declarative and interrogative contrast is important to remember for distinguishing それか and それとも and that か can be seen in both situations when listing noun phrases.
I will eat sushi or sashimi.
Grammar Note: か is not necessary after sashimi. Adding it would be old-fashioned.
I'll eat sushi this evening. Or, I'll eat French cuisine.
Will you write it by hand? Or, will you type it?
I'll cook. Or, I'll do the cleaning.
Practice: Translate the following. You may use a dictionary.
1. A nation like Japan or China.
2. I'll eat fish. Or, I'll eat pizza.
3. Will you go next month? Or, will you go next week?
4. He is around 20 years old.
5. Is he smart?
"Whether (or not)" is "か（どう）か". どう may only be added when the embedded question doesn't have a question word like 何 in it. When just か is used, the "not" is implied.
It is doubtful that he is his little brother.
Do you know if she is coming to the party or not?
I don't know whether or not I'll be able to finish my homework by tomorrow.
“Is tomorrow's weather going to be good?” “Uh, I don't know if it's going to be good weather or not”.
It is unknown whether the teacher went to the school.
I don't know who he is.
Grammar Note: The だ isn't necessary when followed by か inside a subordinate clause.
Variant Note: かいなか is a very formal variant of かどうか.
知る VS 分かる
分かる = "understand/comprehend", which is intransitive, and is spontaneous. 知る, which is transitive, refers to the event of getting to know something. 分かる describes the state of having information and being able to understand it.
知る in the negative is 知らない and essentially never 知っていない*. 知った is the past and 知っている equates to "knowing". In the non-past form, it means know as in "to realize; find out". 知っていない isn't deemed acceptable because 知らない is existential in nature, so there is no need for ~ている, which establishes a state.
I don't understand at all.
Hear one, and know ten.
A word is enough for a wise man.
13. まだ何も知りません。(Sounds stronger)
I still don't know anything.
I still don't understand anything.
*: There are instances when 知っていない is used, but know that the basic negative is 知らない.
Odd Idiom Note: しらが切る means "to act like you don't know something when you do" and the しら comes from 知らない. Set phrases are weird.
AかBないか: No More Than
This usage is exclusively used with counter phrases. As the examples below suggest, A and B are the same verbal expression in the affirmative and negative form respectively.
It costs no more than 2,000 yen.
The number of steps is no more than 1000.
He's no more than fifty years old.
または, rarely written as 又は, is used in situations such as when you want to express tolerance/allowance of either options presented or when out of two things you take one and get rid of the other.
To inform by either phone or telegram.
To either prepare meat or fish.
To put a 〇 to A or B.
Reminder Note: As for または, it gives the sense that either is fine.
もしくは, rarely written in 漢字 as 若しくは, is used in limited situations where you choose something out of several options.
Writing with a fountain pen or a ballpoint pen.
To contact via letter or phone.
Remember Note: もしくは should only be used if the options are not significantly different.
あるいは, rarely in 漢字 as 或（い）は, is used in situations where you are showing that things are alternate or both simultaneous, but it is not normally used in showing permission/allowance.
To either report the interview results by oral representation or essay form.
A capital city like Tokyo or Seoul.
Note: As for あるいは, the items must be of the same kind.
ないし, rarely spelled in 漢字 as 乃至, doesn't merely suggest A or B but A and B and what's in between. This is quite different from the other options. So, pay attention to this.
North or northeast
Etymology Note: As the characters show, this is not a combination of the negative ない and the particle し.
Reminder Note: All of these are rather formal and literary and would be replaced by か in the spoken language.