Ona trči svaki dan ujutro u parku.

You can drop it. Croatian is a pro‑drop language, so the verb ending already shows person/number. Use Ona when you need clarity or emphasis/contrast.

• Neutral: Trči svaki dan ujutro u parku.
• Emphasis/contrast: Ona trči, a on hoda.

Trči is 3rd person singular present of trčati (to run). Present tense:

• ja trčim
• ti trčiš
• on/ona/ono trči
• mi trčimo
• vi trčite
• oni/one/ona trče

No. The simple present covers both ongoing and habitual actions. Context words do the work:

• Habitual: (Ona) trči svaki dan ujutro…
• Ongoing: (Ona) sada trči u parku.

For a one‑off completed act you’d use a perfective verb (e.g., potrčala je = she started to run).

Both are correct:

• svaki dan ujutro = every day, in the morning (explicitly daily + time of day)
• svako jutro / svakog jutra = every morning (already implies daily) Stylistically, svako jutro is shorter and very common.

They mean the same (every day). Grammar/feel:

• svaki dan: Accusative-of-time; very common, neutral.
• svakog dana: Genitive; slightly more formal/literary or emphatic. Both are fine here.

In standard Croatian, the adverb is written as one word: ujutro (in the morning).

• ujutru is Serbian.
• ujutra can mean “in the mornings” (habitually), but is less common in Croatian.
• jutrom (instrumental) also means “in the mornings” and is idiomatic: Jutrom trči u parku.

Because of motion vs. location:

• u
  • Locative = location (in/at): u parku = in the park.
• u
  • Accusative = direction (into/into): u park = into the park. Your sentence describes where the running happens (location), so Locative is required.

Parku is Locative singular of park (masculine). Many masculine nouns take -u in the Locative singular after u/na when indicating location:

• u gradu (in the city), u selu (in the village), u kinu (at the cinema), u parku (in the park).

You can, but the nuance changes:

• u parku = in the park (neutral location).
• po parku = around/all over the park (movement within the area, dispersed path). For a general jogging location, u parku is the neutral choice.

With parks, use u parku. Rough guide:

• u (in): enclosed or defined spaces/volumes (u parku, u školi, u kući).
• na (on/at): surfaces, open venues, events (na plaži, na trgu, na stadionu, na koncertu). There are idiomatic exceptions, but this works here.

Croatian word order is flexible; information structure dictates placement. All of these are natural, with slightly different focus:

• Ona trči svaki dan ujutro u parku. (neutral)
• Svako jutro trči u parku. (time is fronted)
• U parku trči svaki dan ujutro. (location is emphasized)
• Ona svaki dan ujutro trči u parku. (time slot grouped before the verb)

Croatian has no articles; u parku can mean either “in the park” or “in a park.” Add a determiner if needed:

• u tom parku (in that park)
• u našem parku (in our park)

In the present tense, no gender marking appears. Gender shows in past/participle forms:

• Jučer je trčala u parku. (she ran; feminine)
• Jučer je trčao u parku. (he ran; masculine)

Yes, two concise, very natural options:

• Svako jutro trči u parku.
• Trči u parku svako jutro. Both mean “She runs in the park every morning.”