Learn Hardcore Indonesian: Saya berdiskusi singkat dengan kolega tentang target harian. - I have a brief discussion with a colleague about the daily target.

ber- makes an intransitive verb that means to engage in the activity: berdiskusi = to have a discussion. It does not take a direct object.
mendiskusikan is transitive and takes a direct object: to discuss something.

Examples:

Correct with topic marker: Saya berdiskusi tentang target harian (dengan kolega).
Incorrect without a preposition: Saya berdiskusi target harian. (unnatural)
Correct transitive: Saya mendiskusikan target harian dengan kolega.
Common alternative: Kami membahas target harian. (simpler, very natural)

Is berdiskusi singkat natural, or should I say sebentar?

Both are acceptable.

berdiskusi singkat sounds a bit more formal/literary.
berdiskusi sebentar is very natural in everyday speech.
You can also say berdiskusi secara singkat if you want an explicitly adverbial form.

Can I say Saya diskusi singkat (without ber-)?

Yes, in casual speech Indonesians often drop prefixes on certain verbs. Colloquial examples:

Saya diskusi bentar sama kolega soal target harian. In formal writing or careful speech, prefer berdiskusi.

How do I say with my colleague vs with a colleague? Do I need to mark singular/plural?

With my colleague: dengan kolega saya or dengan rekan kerja saya.
With a colleague (unspecified): dengan seorang kolega.
With several colleagues: dengan beberapa kolega or dengan para kolega (formal).
You can also say dengan kolega and let context decide singular vs plural.

What’s the difference among kolega, rekan kerja, and teman kerja?

Do I have to use tentang? Are soal, mengenai, or perihal okay?

All are fine; they differ in register:

tentang: neutral and common.
mengenai: slightly more formal.
perihal: formal/written.
soal: informal/colloquial. Examples: berdiskusi tentang/soal/mengenai/perihal target harian.

Where does singkat go? Could it come before the verb?

Place it after the verb: berdiskusi singkat. Pre-verbal singkat berdiskusi is unnatural. If you want a noun phrase, use:

Can I use bersama instead of dengan?

Yes:

berdiskusi dengan kolega (with a colleague) is neutral.
berdiskusi bersama kolega emphasizes doing it together and is slightly more formal/stylistic. Both are widely used.

How would I make the sentence sound more casual or more formal?

Is target harian singular or plural? How do I specify it?

Indonesian doesn’t mark plural by default; target harian can mean one or more targets depending on context. To be explicit:

One: satu target harian.
Several: beberapa target harian. Reduplication (target-target) is grammatically possible but sounds odd with this loanword; use beberapa instead.

What does harian come from? Can I use sehari-hari?

harian is derived from hari (day) and means daily (scheduled/periodic), as in target harian, koran harian.
sehari-hari means every day/as a habit (day-to-day). You wouldn’t normally say target sehari-hari; stick with target harian.

Can I drop Saya? What about Aku or Gue?

Subject pronouns can be dropped if context is clear: Berdiskusi singkat dengan kolega tentang target harian.
saya: polite/formal.
aku: neutral/informal with peers.
gue: very informal Jakartan slang. Match the register to your audience.

How do I make the object the focus (passive or topicalized)?

Passive: Target harian didiskusikan bersama kolega. or Target harian dibahas bersama kolega.
Topic-fronting: Tentang target harian, saya berdiskusi singkat dengan kolega. Passive is common in formal reports; topic-fronting is also natural.

How do I add time markers like earlier or just now?

Place them flexibly (before the subject, after the subject, or before the verb):