Learn Hardcore Norwegian: Jeg gjør yoga hjemme om kvelden.

Jeg trener yoga – understood, but sounds a bit odd. trener is more for sports/exercise in general:
- Jeg trener fotball. – I practice football.
- Jeg trener på treningssenter. – I work out at the gym.
Jeg praktiserer yoga – correct, but sounds formal/technical, like talking about a discipline or spiritual practice.

So for normal conversation, stick with Jeg gjør yoga.

Why is there no article before yoga? Why not jeg gjør en yoga?

Yoga is treated as an uncountable activity here, like sport, trening (exercise), or lekser (homework).

In Norwegian you normally do not use an article with activities:

Jeg gjør yoga. – I do yoga.
Jeg spiller fotball. – I play football.
Jeg gjør lekser. – I do homework.

Using en/ei/et would sound like you are talking about a single instance of a countable object, which is not how yoga is used here. So jeg gjør en yoga is incorrect in this context.

What exactly does hjemme mean here, and how is it different from hjem?

Both relate to home, but they are used differently:

hjemme = at home (a state/location)
hjem = home (movement towards home)

Examples:

Jeg er hjemme. – I am at home.
Jeg gjør yoga hjemme. – I do yoga at home.
Jeg drar hjem. – I am going home.
Jeg går hjem etter jobb. – I walk home after work.

So in your sentence, you are describing where you do yoga (location), so hjemme is the correct form.

What does om kvelden mean exactly? Is it one specific evening or evenings in general?

Om kvelden usually means in the evening / in the evenings as a habitual or general time.

So:

Jeg gjør yoga hjemme om kvelden.
= I (generally) do yoga at home in the evenings.

It does not mean only tonight; it suggests a regular pattern or a typical time of day.

How is om kvelden different from i kveld?

om kvelden = in the evening / in the evenings (in general, habitually)
- Jeg gjør yoga hjemme om kvelden.
  I usually do yoga at home in the evening(s).
i kveld = this evening (today, specific)
- Jeg gjør yoga hjemme i kveld.
  I am doing yoga at home this evening.

So om kvelden = general routine,
i kveld = tonight / this specific evening.

Can I say på kvelden instead of om kvelden? Is there a difference?

Both om kvelden and på kvelden are used in Norwegian and both can mean in the evening.

om kvelden is very common for a habitual action:
Jeg gjør yoga hjemme om kvelden.
på kvelden can also be used, and many speakers will say:
Jeg gjør yoga hjemme på kvelden.

The difference is small; om kvelden is slightly more typical as a neutral description of routine, but på kvelden does not sound wrong. You will hear both.

Why is it kvelden (with -en) and not just kveld?

Kveld is a masculine noun:

indefinite: en kveld – an evening
definite: kvelden – the evening

In time expressions, Norwegian often uses the definite form:

om morgenen – in the morning
om ettermiddagen – in the afternoon
om kvelden – in the evening
om natten – at night

So om kvelden follows this pattern: literally in the evening but understood as a general time period in the evenings.

Is the word order fixed? Could I say Jeg gjør hjemme yoga om kvelden?

The natural word order is:

Jeg gjør yoga hjemme om kvelden.
(subject – verb – object – place – time)

Jeg gjør hjemme yoga om kvelden is not natural Norwegian; hjemme cannot easily go between gjør and yoga like that.

However, you can move the time or place phrase to the front for emphasis or style:

Om kvelden gjør jeg yoga hjemme.
Hjemme gjør jeg yoga om kvelden.

These are grammatically correct, but the neutral, most common version is the original:
Jeg gjør yoga hjemme om kvelden.

If I want to say this is my habit, is the present tense gjør enough, or do I need extra words?

The simple present tense gjør already expresses a habitual action in Norwegian.

Jeg gjør yoga hjemme om kvelden.
= I (regularly) do yoga at home in the evening(s).

You do not need extra words like usually to show it is a habit. The combination of present tense and the time phrase om kvelden clearly gives a habitual meaning.

You can add adverbs if you want nuance:

Jeg pleier å gjøre yoga hjemme om kvelden. – I usually tend to do yoga at home in the evening.
Jeg ofte gjør yoga hjemme om kvelden. is wrong word order; correct is:
Jeg gjør ofte yoga hjemme om kvelden.

Where would I put ikke if I want to say I do not do yoga at home in the evening?

The normal place for ikke in this sentence is after the verb:

Jeg gjør ikke yoga hjemme om kvelden.
= I do not do yoga at home in the evening.

Basic pattern:
subject – verb – ikke – object – place – time

Examples:

Jeg gjør ikke lekser hjemme. – I do not do homework at home.
Jeg trener ikke på lørdager. – I do not work out on Saturdays.

Could I add liker and say something like I like to do yoga at home in the evening?

Yes. The natural Norwegian sentence would be:

Jeg liker å gjøre yoga hjemme om kvelden.
= I like to do yoga at home in the evening.

Structure:

Jeg liker – I like
å gjøre yoga – to do yoga
hjemme om kvelden – at home in the evening

You still keep the same place and time expression at the end.

Is this sentence informal, formal, or neutral? Would you really say this in everyday Norwegian?

Jeg gjør yoga hjemme om kvelden. is neutral and natural Norwegian.

Fine in spoken language.
Fine in written language.
Works both in casual conversation and in more neutral/formal contexts (email, text, etc.).

It sounds like something a native speaker could easily say about their routine.

How do you pronounce gjør, hjemme, and kvelden?

Approximate pronunciations (Standard East Norwegian, rough English hints):

gjør
- IPA: /jøːr/
- Like yur in “your”, but with lips rounded and a clearer y sound.
hjemme
- IPA: /ˈjɛmːə/
- Sounds roughly like “YEM-meh”
- The h is silent; hj = y sound.
kvelden
- IPA: /ˈkvɛlən/ or /ˈkvɛɾn̩/ (depending on dialect)
- Roughly “KVEL-len”
- kv together as in “kv” in “kvetch” (k + v)
- e like in “bed”.

These are approximations; real pronunciation will vary slightly by dialect.