היא עדיין לא יודעת אם המקצוע הזה מתאים לה, ולכן היא שואלת הרבה על התפקיד.

Because the subject is היא, which is she. In Hebrew, present-tense verb forms agree with gender and number.

So:

• היא יודעת / שואלת = feminine singular
• הוא יודע / שואל = masculine singular

This is very normal in Hebrew present tense.

In Hebrew, the verb to be is usually omitted in the present tense.

So המקצוע הזה מתאים לה literally looks like this profession suitable for her, but it means this profession is suitable for her or suits her.

In past or future, Hebrew would use forms of היה:

• המקצוע הזה היה מתאים לה = this profession was suitable for her
• המקצוע הזה יהיה מתאים לה = this profession will be suitable for her

Because מתאים agrees with המקצוע הזה, not with היא.

The thing that is suitable is המקצוע. Since מקצוע is masculine singular, Hebrew uses מתאים.

Compare:

• המקצוע הזה מתאים לה = this profession suits her
• העבודה הזאת מתאימה לה = this job/work suits her

Here, עבודה is feminine, so the word changes to מתאימה.

לה means to her or for her, depending on how you translate it into natural English.

It is made from:

• ל־ = to/for
• היא = she/her

With מתאים, Hebrew normally uses ל־:

• זה מתאים לי = this suits me
• זה מתאים לך = this suits you
• זה מתאים לה = this suits her

So the pattern is basically X מתאים ל-Y = X suits Y.

Here it means whether.

After verbs like know, ask, check, or see, Hebrew often uses אם to introduce an indirect yes/no question:

• אני לא יודע אם... = I don’t know whether...
• היא שואלת אם... = she asks whether...

The same word אם can also mean if, so context tells you which meaning is intended.

אם is often used for whether inside a larger sentence.

האם is a marker used mainly for a direct yes/no question, often in more formal Hebrew.

Compare:

• היא לא יודעת אם המקצוע הזה מתאים לה = she doesn’t know whether this profession suits her
• האם המקצוע הזה מתאים לה? = does this profession suit her?

So in your sentence, אם is the right choice.

It can correspond to either one in English, depending on what sounds natural in context.

So:

• היא עדיין לא יודעת can be understood as she still doesn’t know
• or she doesn’t know yet

Hebrew עדיין לא covers that idea very naturally.

Because in Hebrew, demonstratives like this and that usually come after the noun.

So:

• המקצוע הזה = this profession
• הספר הזה = this book
• העבודה הזאת = this job/work

This is different from English, where this comes before the noun.

Also, notice that the noun is definite:

• המקצוע הזה not
• מקצוע הזה

לכן means therefore, so, or for that reason.

The ו־ at the beginning means and.

So ולכן means something like:

• and therefore
• and so
• which is why

It connects the two parts of the sentence logically: she doesn’t know yet whether the profession suits her, so she asks a lot about the role.

Because על התפקיד means about the role, and that is the topic of what she is asking about.

Hebrew often uses:

• לשאול על... = to ask about...

So:

• היא שואלת על התפקיד = she asks about the role

If you want to mention the person she is asking, that person can be a direct object:

• היא שואלת את המראיין על התפקיד = she asks the interviewer about the role

So את would mark the person being asked, not the topic.

הרבה here means a lot.

So היא שואלת הרבה means she asks a lot or she asks many questions.

Its position after the verb is very natural in Hebrew:

• היא קוראת הרבה = she reads a lot
• הוא עובד הרבה = he works a lot
• היא שואלת הרבה על התפקיד = she asks a lot about the role

Hebrew does not need to say שאלות explicitly here, although you could say:

• היא שואלת הרבה שאלות על התפקיד = she asks a lot of questions about the role

They are related, but not the same.

• מקצוע = profession, field, occupation
• תפקיד = role, position, function, specific job duties

So the sentence suggests:

• she is unsure whether this profession/field is right for her
• therefore she asks a lot about the specific role/position

That distinction is very natural in Hebrew.