Round your lips into a tight circle. Lift the back of your tongue toward the soft palate and add voice.

Americans pronounce witnesses as WIHT-nuh-suhz (/ˈwɪtnəsəz/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "The defense attorney gathered witnesses to support her client" or "The witnesses were sequestered so they could not hear other testimonies" — more examples below.
Record yourself saying "witnesses" and play it back. The mic stays on your device — nothing's uploaded.
3 syllables, 8 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
Round your lips into a tight circle. Lift the back of your tongue toward the soft palate and add voice.

Drop your jaw slightly with relaxed lips. Touch the tongue tip behind the bottom front teeth and arch the top-front toward the roof.

Touch the tip or front edge of your tongue to the roof of your mouth just behind your teeth. Keep your jaw relaxed. Stop the air, then release with a puff.

Click any sentence to see the full breakdown — every link, every reduction, every flap-T.
The textbook way isn't wrong — it's just not how anyone actually says it.
In "witnesses", the "t" is not released — the articulators get into position but hold without the burst of air. Air stops but there's no release burst — the articulators hold position.
Stress falls on the first syllable, not the others. Stretch WIHT — keep everything else short and quick.
Don't pronounce the first syllable too fully. The unstressed syllable reduces to a schwa — the lazy "uh" sound — in casual speech.