The Jan 6 hearing is not a criminal trial, there is no judge, jury, or lawyers for the prosecution or the defense, just like there are none in a grand jury hearing which is also not a trial. Hence no cross examinations of witnesses take place, just like there is none in a grand jury hearing . The committee has two jobs, the investigative process which is to acquire information and the hearing in which they present that information.
The Jan 6 hearings show what happened in the weeks after the 2020 election and on the day of the attack. They show the public “how one thing led to another, how one line of effort to overturn the election led to another and ultimately led to terrible violence,” as committee member Adam Schiff put it on June 5, 2022.
Hearings also serve as a kind of preemptive justification for specific legal and legislative actions that may follow the investigation. For example, if the committee does end up recommending criminal charges against Trump and his allies, the hearings have already explained the legitimacy of these charges to the public. If the committee makes legislative recommendations to reform elections, the public will have a better idea of why these changes are necessary.
If criminal charges against Trump and his allies are made by the DOJ there will be a criminal trial with lawyers for the defense and prosecution, and cross examination etc will take place there.