Short answer
Psalm 119 does not name an author in the Hebrew text, so its human author is uncertain. From an evangelical perspective the most likely candidates proposed are a post‑exilic scribe or Torah‑teacher (often identified with Ezra) or an otherwise anonymous Levite/poet. Many evangelicals simply acknowledge the uncertainty while affirming the psalm’s divine inspiration and practical message.

Why Ezra or a post‑exilic scribe is often suggested
– The content strongly emphasizes the Torah: law, statutes, precepts, testimonies, commandments and the study and delighting in God’s Word. That focus fits someone whose life and ministry centered on teaching and restoring the law (Ezra 7:10: “He set his heart to study the Law of the LORD and to do it and to teach his statutes and rules in Israel”).
– Psalm 119’s careful acrostic structure (22 stanzas corresponding to the Hebrew alphabet) and polished poetic form suggest a learned scribe or teacher skilled in literary composition.
– Many scholars (including conservative evangelical commentators) see the theology and concerns of the psalm—communal fidelity to the law, repentance, preservation of the people under God’s Word—as consonant with the post‑exilic period when Israel was reestablishing covenant life under the Torah.

Why some still allow for Davidic or anonymous authorship
– The Psalter contains many Davidic psalms, and Jewish and Christian traditions sometimes attribute unattributed psalms to David by default. However, Psalm 119 has no superscription saying “of David,” so that attribution is speculative.
– Because the psalm itself concentrates on God’s Word more than on historical circumstance, many evangelicals are content with calling the human author “anonymous” and focusing on the theological message rather than settling the historical identity.

An evangelical reading of Psalm 119:18
– Psalm 119:18 (“Open my eyes, that I may behold wondrous things from your law.”) is typically read devotionally and theologically: it’s a prayer for illumination. Evangelicals emphasize that while human authorship may be uncertain, Scripture is God‑breathed (2 Timothy 3:16) and needs the Spirit’s illumination (1 Corinthians 2:14–16, John 14:26). Verse 18 becomes a model prayer asking God to enable understanding, to reveal Christ and truth, and to make the law (and the whole Bible) life‑giving and transformative.
– Pastoral application commonly taught in evangelical circles: pray for understanding before reading Scripture, value Scripture as the means of sanctification, and see the Bible’s commands as gracious guidance empowered by the Spirit.

Recommended evangelical resources
– ESV Study Bible notes on Psalm 119 (conservative, helpful background and application).
– Derek Kidner, Psalms commentary (brief, pastoral, evangelical).
– C. H. Spurgeon, “Treasury of David” (classic devotional exposition).
– Articles in The Gospel Coalition or Desiring God often discuss Psalm 119 devotionally and treat the illumination theme of v. 18.

Summary
Most evangelicals will say Psalm 119’s precise human author is uncertain but that the strongest internal case points to a learned, devotional Torah‑teacher—commonly associated with Ezra or a post‑exilic scribe—while the real emphasis should be on the psalm’s inspired message: a heartfelt love for God’s Word and a prayer for divine illumination (as in v. 18).