בפיקוח ההנדסי התגלה ליקוי בנייה.

ב־ is the preposition in, during, under, or sometimes as part of, depending on context.

So בפיקוח ההנדסי can mean something like:

• in the engineering inspection
• during the engineering supervision
• under the engineering oversight

The exact English wording depends on the situation, but the basic idea is that something was discovered in the course of or through engineering inspection/supervision.

It actually is definite here.

The full form is:

• ב + הפיקוח ההנדסי

But in Hebrew, when certain prepositions attach to a noun with ה־ (the), the forms contract:

• ב + ה... becomes בַ / בַּ...
• in unpointed modern spelling, this is often just written ב...

So בפיקוח ההנדסי is really functioning as in the engineering inspection/supervision.

Also, adjectives in Hebrew usually match the noun in definiteness, so:

• פיקוח הנדסי = engineering supervision / an engineering inspection
• הפיקוח ההנדסי = the engineering supervision / inspection
• בפיקוח ההנדסי = in the engineering supervision / inspection

התגלה means was discovered, was revealed, or came to light.

It comes from the root ג־ל־ה, which is connected with revealing or uncovering.
In this sentence, the form is a past-tense, masculine singular form in the Nif'al pattern, which often has a passive or middle meaning.

So:

• גילה = he discovered / revealed
• התגלה = it was discovered / it came to light

In this sentence, התגלה matches ליקוי because ליקוי is masculine singular.

Because the subject is ליקוי בנייה.

The head noun is ליקוי, and ליקוי is:

• masculine
• singular

So the verb agrees with it:

• התגלה ליקוי בנייה = a construction defect was discovered

If the subject were feminine singular, you would expect a feminine verb form.
If it were plural, the verb would normally be plural too.

ליקוי בנייה means construction defect, building defect, or defect in construction.

It is a noun + noun structure, often called a construct relationship in Hebrew, even though modern Hebrew often uses such combinations quite flexibly.

Here:

• ליקוי = defect / flaw
• בנייה = construction / building

Together, they mean a defect related to construction.

A natural English translation is usually:

• a construction defect
• a building defect

Hebrew often prefers a compact noun + noun structure where English might use of.

So instead of:

• a defect of construction

Hebrew commonly says:

• ליקוי בנייה

This is very natural and common in formal or technical language.

Using של is possible in some contexts in Hebrew, but here it would sound less natural and less concise.
For this kind of fixed or professional expression, ליקוי בנייה is the normal choice.

Because Hebrew often allows, and frequently prefers, verb-first word order, especially in formal writing or reporting style.

So:

• התגלה ליקוי בנייה = literally was discovered a construction defect
• natural English: a construction defect was discovered

This verb-before-subject order is very normal in Hebrew.

You could also reorder it for emphasis, for example:

• ליקוי בנייה התגלה בפיקוח ההנדסי

That is still grammatical, but it shifts the focus slightly.

All of those can be possible depending on context.

פיקוח can mean:

• supervision
• oversight
• inspection
• monitoring

So בפיקוח ההנדסי may suggest:

• something discovered during an engineering inspection
• something found through engineering oversight
• something noticed under engineering supervision

If the sentence comes from construction, safety, or legal reporting, during the engineering inspection or in the engineering supervision process may fit best.

Because ליקוי בנייה is not a direct object here.

In this sentence, ליקוי בנייה is the subject of התגלה:

• A construction defect was discovered

Hebrew uses את only before a definite direct object.

Compare:

• המפקח גילה ליקוי בנייה = The inspector discovered a construction defect
  No את, because the object is indefinite.

• המפקח גילה את ליקוי הבנייה = The inspector discovered the construction defect
  Here את appears because the object is definite.

But in your sentence, the structure is passive-like/intransitive:

• התגלה ליקוי בנייה = A construction defect was discovered

So there is no direct object marker.

Yes, in English you could sometimes translate it more actively depending on style, even though the Hebrew uses התגלה.

Possible translations include:

• A construction defect was discovered during the engineering inspection.
• The engineering inspection revealed a construction defect.

The second version is more active in English, but it slightly reshapes the sentence.
The Hebrew original keeps the focus on the defect being discovered, not on who discovered it.

So the most direct translation is usually the passive-style one:

• A construction defect was discovered during the engineering inspection.