Ich kenne ihren Ehemann.

German usually uses kennen for being acquainted or familiar with a person, place, or thing.

• Ich kenne ihren Ehemann. = I am acquainted with / I know her husband.
• Ich weiß ... is used for facts or information.

Compare:

• Ich kenne ihn. = I know him.
• Ich weiß, wo er wohnt. = I know where he lives.

So with a person as the object, kennen is the normal choice.

Ihren is a possessive determiner, meaning something like her, their, or in other contexts formal your. In this sentence, it is in the accusative masculine singular form.

Why that form?

• Ehemann is masculine: der Ehemann
• It is the direct object of kennen
• A masculine direct object takes the accusative
• So ihr- becomes ihren

A quick comparison:

• ihr Ehemann = her husband / their husband as subject
• ich kenne ihren Ehemann = I know her husband / their husband as object

Yes. Written as ihren with a lowercase i, it can mean:

• her
• their

Context tells you which one is meant.

For example:

• Ich kenne ihren Ehemann. could mean I know her husband.
• It could also mean I know their husband, depending on context.

Formal your would normally be written with a capital letter: Ihren. Since this sentence has ihren, it is not the formal your.

Because it is the direct object of kennen.

In the sentence:

• Ich = subject
• kenne = verb
• ihren Ehemann = direct object

German marks many masculine direct objects with a special accusative form. That is why you see:

• der Ehemann in the nominative
• den Ehemann in the accusative

With a possessive word, that becomes:

• ihr Ehemann
• ihren Ehemann

Because ihren already fills that slot.

In German, words like mein, dein, sein, ihr, unser work like determiners. They function in a similar position to articles such as der, die, das, den.

So German says:

• der Ehemann = the husband
• ihr Ehemann = her husband
• ihren Ehemann = her husband in the accusative

You do not combine them like ihren den Ehemann.

Because all nouns are capitalized in German.

So:

• ich is not capitalized unless it begins a sentence
• kenne is a verb, so it is not capitalized
• Ehemann is a noun, so it is capitalized

This is one of the most noticeable spelling differences between German and English.

This is the standard German main-clause word order:

• subject
  • verb
    • object

So:

• Ich = subject
• kenne = conjugated verb
• ihren Ehemann = object

German main clauses usually put the conjugated verb in the second position. Here, the subject comes first, so the verb naturally comes right after it.

The base form is kennen.

Kenne is the 1st person singular present tense form:

• ich kenne = I know
• du kennst = you know
• er/sie/es kennt = he/she/it knows

So kenne matches the subject ich.

Yes, Ehemann does mean husband, but it can sound a bit more formal or explicit than just Mann, depending on context.

German also often uses:

• mein Mann = my husband

Even though Mann literally means man, in the right context it can also mean husband.

So:

• ihr Ehemann = her husband
• ihr Mann = her husband

Both are possible, but Ehemann is more specific and leaves no doubt.

Because ich is in the nominative form and the verb is conjugated to match it:

• ich kenne

Also, in a simple sentence like this, the first noun/pronoun before the verb is very often the subject.

So the sentence structure is straightforward:

• Ich = I
• kenne = know
• ihren Ehemann = her husband / their husband

For many English speakers, ich is tricky. The ch sound in ich is not like English ch in chair.

It is the ich-Laut, a soft sound made high in the mouth, something like a gentle hiss after i.

A rough guide:

• ich sounds a bit like ish to many beginners, but that is only approximate
• it is not ik
• it is not itch

Also:

• kenne has a clear k
• ihren begins with a long ee sound
• Ehemann starts with Eh-, roughly like AY-eh-mahn if said carefully, though exact German pronunciation is better learned from audio

If you want, I can also break down the full pronunciation of the whole sentence word by word.