xíngli bùshì zài xīnjū lǐ, jiùshì zài huòchē shàng.

It means either... or....

So:

• 行李不是在新居里，就是在货车上。
• The luggage is either in the new home or on/in the truck.

This pattern presents two possibilities, and the speaker is saying that one of them must be true.

Great question. In this pattern, 不是……就是…… is a fixed expression meaning either... or.... The 是 here is not functioning like the normal to be in English.

The actual location part is:

• 在新居里
• 在货车上

In Chinese, location is usually expressed with 在 + place.

So in this sentence:

• 不是……就是…… = the either...or... frame
• 在新居里 / 在货车上 = the two location options

Because each half of the either...or... structure needs its own full location phrase.

So the sentence is built like this:

• 不是 在新居里
• 就是 在货车上

Each option is complete on its own. Repeating 在 makes the sentence clear and balanced.

If you left out the second 在, it would sound incomplete or unnatural here.

Because Chinese uses different location words depending on how something relates to the place.

• 里 = inside
• 上 = literally on top of, but it is also commonly used for vehicles

So:

• 在新居里 = inside the new home
• 在货车上 = on/in the truck

With vehicles, Chinese often uses 上, even when English would say in:

• 在车上 = in the car / on the vehicle
• 在飞机上 = on the plane
• 在船上 = on the boat

So 在货车上 is completely normal.

It can mean either, depending on context.

In English, we often distinguish:

• on the truck = on top of it
• in the truck = inside it

But in Chinese, 在货车上 is a common way to say something is on the truck / in the truck / loaded onto the truck, especially when talking about transport.

So here it most likely means the luggage is on the moving truck / loaded in the truck.

Because Mandarin does not usually use articles like a or the the way English does.

So:

• 行李 can mean luggage / the luggage
• 新居 can mean new home / the new home
• 货车 can mean truck / the truck

The exact meaning is understood from context.

行李 is a collective noun, like luggage in English.

So it does not normally change for singular or plural:

• 行李 = luggage / baggage

If you want to count pieces of luggage, you would use a measure word, for example:

• 一件行李 = one piece of luggage
• 两件行李 = two pieces of luggage

In your sentence, 行李 just means the luggage in general.

Both can refer to a new home, but they feel a little different.

• 新家 = more common and everyday
• 新居 = more formal, written, or slightly elegant

新居 is often used in contexts like moving, settling into a new residence, or even housewarming situations.

So in this sentence, 新居 sounds a bit more polished than 新家.

In 行李, it is pronounced:

• xíngli

The second syllable li is usually in a neutral tone.

The character 行 has multiple pronunciations in Chinese, including:

• xíng = okay, to go, workable
• háng = line, row, profession

In the word 行李, it is always xíng.

This is something learners just have to memorize word by word, because many Chinese characters are multiple-pronunciation characters.

This is because of tone sandhi.

Normally:

• 不 = fourth tone (bù)

But when 不 comes before another fourth-tone syllable, it usually changes to second tone in pronunciation:

• 不是 is pronounced bú shì

It is often still written as bùshì in basic materials, but in natural speech you will usually hear:

• búshì

Yes, often you can.

For example:

• 行李要么在新居里，要么在货车上。

This also means The luggage is either in the new home or on the truck.

A rough difference is:

• 不是……就是…… can sound a bit like the speaker is narrowing it down to two likely possibilities
• 要么……要么…… is a straightforward either...or... pattern

In many everyday situations, both work.

Usually, for simple location statements, Chinese prefers:

• 行李在新居里。

Adding 是 before a location is usually unnecessary unless you are using a special emphatic structure.

So:

• 行李在新居里。 = normal
• 行李是在新居里。 = possible in special contexts, but not the basic default

In your original sentence, the 是 appears because of the fixed pattern 不是……就是……, not because location normally needs 是.

The basic location pattern is:

• Subject + 在 + Place

Examples:

• 行李在新居里。 = The luggage is in the new home.
• 行李在货车上。 = The luggage is on/in the truck.

Your full sentence simply puts two of these location phrases into the 不是……就是…… pattern:

• 行李 不是 在新居里，就是 在货车上。

So the structure is:

• Subject + either location A or location B