Der Handwerker erklärt, dass er das Rohr prüfen kann, wobei er sehr vorsichtig arbeitet.

The tradesperson explains that he can check the pipe, while working very carefully.

Breakdown of Der Handwerker erklärt, dass er das Rohr prüfen kann, wobei er sehr vorsichtig arbeitet.

• er: he
• arbeiten: to work
• sehr: very
• können: can
• dass: that
• erklären: to explain
• prüfen: to check
• der Handwerker: the tradesperson
• das Rohr: the pipe
• wobei: while / whereby
• vorsichtig: careful / carefully

Questions & Answers about Der Handwerker erklärt, dass er das Rohr prüfen kann, wobei er sehr vorsichtig arbeitet.

Why is there a comma before dass?

In German, a dass-clause is a subordinate clause, and it is always separated by a comma from the main clause.
So: Der Handwerker erklärt, dass ... is standard and mandatory punctuation.

Why does the verb come at the end in dass er das Rohr prüfen kann?

In subordinate clauses (like those introduced by dass), German normally puts the conjugated verb at the end.
With a modal verb construction, the main action is in the infinitive (prüfen) and the conjugated modal goes last:

• ... dass er das Rohr prüfen kann (literally: that he the pipe check can)

What is the grammatical role (case) of der Handwerker and das Rohr?

• der Handwerker is nominative: it’s the subject (the person doing the explaining).
• das Rohr is accusative: it’s the direct object of prüfen (what is being checked).

Why is er used—could it be sie or something else?

er refers back to der Handwerker, which is grammatically masculine (and typically male in meaning, though not necessarily).
If the sentence were about die Handwerkerin (female craftsperson), you’d use sie:

• Die Handwerkerin erklärt, dass sie das Rohr prüfen kann ...

What does wobei mean here, grammatically and in meaning?

wobei introduces another subordinate clause and commonly means something like in doing so / and while doing that / in the process.
It links the second action to the first clause as an accompanying circumstance: he can check the pipe, and while doing that, he works very carefully.

How is wobei different from während?

• während means during/while and is often a straightforward time overlap: while X happens, Y happens.
• wobei often adds a comment about the same overall situation: in the course of that, and in that context.

Here, wobei sounds like an additional detail about how he does the checking, not just a neutral time relation.

Why is there a comma before wobei too?

Because wobei er sehr vorsichtig arbeitet is also a subordinate clause, and German uses commas to set off subordinate clauses.
So both commas (before dass and before wobei) are required.

Could the sentence be written without dass?

Yes. After verbs like erklären, German can sometimes omit dass, especially in speech, and then the subordinate clause has main-clause word order:

• Der Handwerker erklärt, er kann das Rohr prüfen, wobei er sehr vorsichtig arbeitet.
  This is more informal and can feel a bit looser; the dass version is clearer and very common in writing.

Why is it sehr vorsichtig arbeitet (adverb + verb)? Is vorsichtig an adjective here?

Here vorsichtig functions as an adverb describing how he works. In German, many adjectives can be used adverbially without changing form:

• vorsichtig arbeiten = to work carefully
  sehr intensifies it: very carefully.

Is the tense normal here? Why present tense for everything?

Yes. German often uses the present tense for statements about what someone can do and how they do it, especially when it’s general or current.
If you wanted past reporting, you might use past forms (depending on context), e.g. erklärte / hat erklärt, but the present is perfectly natural as a general statement.